The Institute for Quantum Computing (IQC) now offers two different Quantum Innovators workshops to bring together the most promising young postdoctoral fellows.

Participants may choose to attend just their stream, or attend both streams across the five days.

*These workshops held at IQC, University of Waterloo, are partly funded by the Canada First Research Excellence Fund (CFREF) as part of the Transformative Quantum Technologies research initiative.*

## Schedule

Monday, November 6

Tuesday, November 7

Wednesday, November 8

Thursday, November 9

Friday, November 10

Talks Titles and Abstracts

Speakers and Biographies

**Monday, November 6** | **QNC 0101**

**9:00 am** Coffee and Registration

**9:30 am **Opening remarks by IQC Director Norbert Lütkenhaus

**9:40 am** Harriet Apel, University College London

Simulating LDPC code Hamiltonians on 2D lattices

**10:25 am** Fermi Ma, Simons Institute, University of California, Berkeley

A one-query lower bound for unitary synthesis and breaking quantum cryptography

**11:10 am **Break

**11:30 am **James Bartusek, University of California, Berkeley

Obfuscation of Quantum Computation

**12:15 pm **Plenary: Clarice Aiello, University of California, Los Angeles

“Quantum Biology”: how nature harnesses quantum processes to function optimally, and how might we control such quantum processes to therapeutic advantage

**1:15 pm** Lunch at St. Jerome’s

**2:30 pm** Vjosa Blakaj, Technical University of Munich

A Transcendental Toolbox in Quantum Information Theory

**3:15 pm** Freek Witteveen, University of Copenhagen

The resource theory of tensor networks

**4:00 pm **Paula Belzig University of Copenhagen

Fault-tolerant entanglement-assisted communication

**4:45 pm** Coffee and snacks QNC 2^{nd} floor kitchen

**Tuesday, November 7 | QNC 0101**

**9:00 am** Coffee

**9:30 am **Matthias C. Caro, Freie Universität Berlin

Classical Verification of Quantum Learning

**10:15 am** João Doriguello, National University of Singapore

Quantum and quantum-inspired algorithms for k-means and Lasso path problems

**11:00 am** Break

**11:20 am** Priyanga Ganesan, University of California, San Diego

A nonlocal game involving quantum graphs

**12:05 pm** Beatriz Dias, Technical University of Munich

Classical simulation of non-Gaussian fermionic circuits

**12:50 pm** Lunch at St. Jerome's

**2:30 pm** Jiahui Liu, Massachusetts Institute of Technology

Another Round of Breaking and Making Quantum Money: How to Not Build It from Lattices, and More

**3:15 pm **Yihui Quek, Massachusetts Institute of Technology

The signal and the noise: learning with random quantum circuits and other agents of chaos

**4:00 pm** Coffee and snacks QNC 2^{nd} floor kitchen

**6:30 pm** Dinner with IQC Faculty at Bauer Kitchen

**Wednesday, November 8 | ****QNC 0101**

**9:00 am** Coffee

**9:30 am** Opening remarks by IQC Director Norbert Lütkenhaus and David Cory

**9:40 am **Alexander Schuckert, Joint Quantum Institute, University of Maryland

Observation of a finite-energy phase transition in a one-dimensional quantum simulator

**10:25 am** Christophe Piveteau, ETH Zürich

Quasiprobability simulation for near-term quantum computing

**11:10 am** Break

**11:30 am** Plenary: Alexey Gorshkov, National Institute of Standards and Technology and University of Maryland

Bound states in photonic and atomic crystals

**12:30 pm** Lunch at St. Jerome’s

**1:45 pm **Academic career panel discussion

**3:00 pm** QNC Lab Tours

**4:00 pm **Poster session with IQC members, QNC 2^{nd} floor kitchen

**5:30 pm **End of day

**Thursday, November 9 | ****RAC1 2009**

**9:00 am** Coffee

**9:20 am** Opening remarks

**9:30 am** Michael Vasmer, Perimeter Institute

Fault-tolerant quantum computing beyond the surface code

**10:15 am** Susanna Todaro, Oxford Ionics

Towards Quasi-Dual Species Operation with Metastable- and Ground-State Qubits in Barium

**11:00 am** Break

**11:20 am **Conor Bradley, University of Chicago

A dual-species Rydberg array

**12:05 pm** Josiah Sinclair, Massachusetts Institute of Technology

Progress towards quantum error correction with a programmable Rydberg array in an optical cavity

**12:50 pm** Lunch at RAC

**2:00 pm** RAC Lab Tours

**4:00 pm **Coffee and snacks

**6:30 pm** Dinner with IQC Faculty at Trio

**Friday, November 10 | ****QNC 0101**

**9:00 am** Coffee

**9:30 am **Sasan V. Grayli, Institute for Quantum Computing

Metamaterial Perfect Absorbers for Sensitive Avalanche Photodiodes in SWIR Region

**10:15 am **Behrooz Semnani, Institute for Quantum Computing

Metasurface structures for control of quantum emitters

**11:00 am** Break

**11:20 am** Aziza Suleymanzade, Harvard University

Quantum network based on color centers in diamond nanocavities

**12:05 pm** Tatsuhiro Onodera, NTT Research Cornell University

Reprogrammable integrated photonic circuits for quantum optics

**12:50 pm** Lunch at St. Jerome’s

**2:00 pm** Maya Miklos, JILA, University of Colorado Boulder

Spin squeezing-enhanced stability in an optical lattice clock comparison at the 10^{-17} level

**2:45 pm** Annie Jihyun Park, Harvard University

Dipolar interactions in a molecular tweezer array

**3:30 pm** Closing remarks

**4:00 pm **Tea time with IQC members, QNC 2^{nd} floor kitchen

## Abstracts

## Simulating LDPC code Hamiltonians on 2D lattices

**Harriet Apel ^{a}** , Nouédyn Baspin

^{b}

^{a}Department of Computer Science, University College London, UK

^{b}School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia

While the existence of good LDPC codes has been demonstrated, this has come at a cost of diverging from the geometrical constraints of many hardware platforms. In this work we use techniques from Hamiltonian simulation theory to build a simulation of LDPC codes using only 2D nearest-neighbour interactions, at the cost of an energy penalty polynomial in the system size. We show that this simulation allows to approximate the ground state of the code Hamiltonian, effectively approximating a [[N, Ω(√ N), Ω(√ N)]] code in 2D. The key ingredient is a new constructive tool to simulate an *l*-long interaction between two qubits by a 1D chain of* l* nearest-neighbour interacting qubits using poly(*l*) interaction strengths. This is an exponential advantage over the existing gadgets for this routine which facilitates the first ϵ-simulation of *arbitrary sparse* Hamiltonian on n qubits with a Hamiltonian on a 2D lattice of *O*(*n ^{2}*) qubits with interaction strengths scaling as

*O*(poly(

*n*, 1/ϵ)).

## A one-query lower bound for unitary synthesis and breaking quantum cryptography

### Fermi Ma, Simons Institute, University of California, Berkeley

The Unitary Synthesis Problem (Aaronson-Kuperberg 2007) asks whether any *n*-qubit unitary* U* can be implemented by an efficient quantum algorithm A augmented with an oracle that computes an arbitrary *Boolean function f _{U}* . In other words, can the task of implementing any unitary be efficiently reduced to the task of implementing any Boolean function?

In this work, we prove a one-query lower bound for unitary synthesis. We show that there exist unitaries U such that no quantum polynomial-time oracle algorithm A^{f} can implement *U*, even approximately, if it only makes one (quantum) query to f. Our approach also has implications for quantum cryptography: we prove (relative to a random oracle O) the existence of quantum cryptographic primitives that remain secure against all one-query adversaries A^{f} . Since such one-query algorithms can decide any language, solve any classical search problem, and even prepare any quantum state, our result suggests that implementing random unitaries and breaking quantum cryptography may be harder than all of these tasks.

To prove this result, we formulate unitary synthesis as an efficient challenger-adversary game, which enables proving lower bounds by analyzing the maximum success probability of an adversary A^{f} . Our main technical insight is to identify a natural spectral relaxation of the one-query optimization problem, which we bound using tools from random matrix theory.

We view our framework as a potential avenue to rule out polynomial-query unitary synthesis, and we state conjectures in this direction.

Based on joint work with Alex Lombardi and John Wright.

## Obfuscation of Quantum Computation

### James Bartusek, University of California, Berkeley

A program obfuscator is a one-way compiler that facilitates hiding secrets inside of fully functioning code. Obfuscation (of classical computation) has been one of the central objects of study in cryptography over the past decade, due to its incredibly wide range of applications. This talk will survey the emerging research topic of obfuscation for quantum computation. We will cover recent progress on constructions and applications, discuss connections with blind and verifiable quantum computation, and present a number of future research directions.

Based on joint works with Giulio Malavolta and with Fuyuki Kitagawa, Ryo Nishimaki, and Takashi Yamakawa.

## Another Round of Breaking and Making Quantum Money: How to Not Build It from Lattices, and More

### Jiahui Liu, Massachusetts Institute of Technology

Public verification of quantum money has been one of the central objects in quantum cryptography ever since Wiesner's pioneering idea of using quantum mechanics to construct banknotes against counterfeiting. So far, we do not know any publicly verifiable quantum money scheme that is provably secure from standard assumptions. In this talk, we provide both negative and positive results for publicly verifiable quantum money.

**In the first part, we give a general theorem, showing that a certain natural class of quantum money schemes from lattices cannot be secure. We use this theorem to break the recent quantum money scheme of Khesin, Lu, and Shor.

**In the second part, we propose a framework for building quantum money and quantum lightning we call invariant money which abstracts some of the ideas of quantum money from knots by Farhi et al. (ITCS'12). The security of this framework also leads to the security for a strengthening of quantum money, where not even the bank can duplicate banknotes.

Joint work with Hart Montgomery and Mark Zhandry.

## A Transcendental Toolbox in Quantum Information Theory

### Vjosa Blakaj, Technical University of Munich

VJOSA BLAKAJ^{1,2} (joint work with Michael M. Wolf^{1,2} and Chokri Manai^{1,2 })

For information-theoretic quantities with an asymptotic operational characterization, the question arises as to whether an alternative single-shot characterization exists, possibly including an optimization over an ancillary system. If the expressions are algebraic and the ancillary system is finite, this leads to semialgebraic level sets. Here we provide criteria to study the semialgebraicity of restricted subsets of Euclidean spaces and apply the obtained results to the set of states where entropic quantities such as von Neumann entropy, relative entropy, mutual information, or R`enyi entropies are fixed. When such level sets are transcendental, our results rule out algebraic single-shot characterizations of the above entropic quantities with a finite ancillary system (e.g., via catalytic transformations). Furthermore, we also analyze the set of reduced states of translation-invariant infinite quantum systems from such a perspective. The set of reduced two-body states of translation-invariant, infinite quantum spin chains can be approximated from inside and outside by matrix product states and marginals of finite systems, respectively. These lead to hierarchies of algebraic approximations which become tight only in the limiting case of infinitely many auxiliary variables. We show that this is necessarily the case for any algebraic approach by proving that the set of reduced states is not semialgebraic. We also show that additional elementary transcendental functions cannot lead to a finitary description.

^{1} Department of Mathematics, School of Computation, Information and Technology, Technical University of Munich, Garching, Germany

^{2 }Munich Center for Quantum Science and Technology (MCQST), Munich, Germany

## The resource theory of tensor networks

### Freek Witteveen, University of Copenhagen

Tensor networks provide succinct representations of quantum many body states and are an important computational tool for strongly correlated quantum systems. Their expressive and computational power is characterized by an underlying entanglement structure, on a lattice or more generally a (hyper)graph, with virtual entangled pairs or multipartite entangled states associated to (hyper)edges. Changing this underlying entanglement structure into another can lead to both theoretical and computational benefits. In this talk I will explain results from arXiv:2307.07394, where we study a resource theory which generalizes the notion of bond dimension to entanglement structures using multipartite entanglement. It is a direct extension of resource theories of tensors studied in the context of multipartite entanglement and algebraic complexity theory, allowing for the application of the methods developed in these fields to tensor networks.

## Fault-tolerant entanglement-assisted communication

### Paula Belzig, University of Copenhagen

Channel capacities quantify the optimal asymptotic rates of sending information over noisy channels where the original message can always be recovered. Usually, the study of capacities assumes that the circuits which the sender and the receiver use for encoding and decoding the information consist of perfect gates without noise. While this assumption is realistic for classical computers, is not believed to be true for quantum devices manufactured in the near-term and even long-term future due to the fragility of quantum information, which is affected by the process of decoherence. Assuming that each gate is affected by an error with a small probability, we use techniques from fault-tolerant quantum computing to prove a coding theorem for a fault-tolerant version of the entanglement-assisted classical capacity, and we prove in particular that this capacity approaches the usual, faultless case for vanishing gate error probability.

## Classical Verification of Quantum Learning

### Matthias C. Caro, Freie Universität Berlin

Quantum data and processing can make classically intractable learning tasks feasible. However, quantum capabilities will only be available to a select few. Thus, reliable schemes that allow classical clients to delegate learning to untrusted quantum servers are required. Building on a recently introduced framework of interactive proofs for classical machine learning, we develop a framework for classical verification of quantum learning. We exhibit learning problems that a classical learner cannot efficiently solve on their own, but that they can efficiently and reliably solve when interacting with an untrusted quantum prover, based on a new quantum data access model that we call "mixture-of-superpositions" examples. We also showcase two scenarios in learning and verification in which these examples do not outperform classical data. Our results demonstrate that the power of quantum data for learning tasks, while not unlimited, can be utilized by classical agents through interaction with untrusted quantum entities.

Quantum and quantum-inspired algorithms for k-means and Lasso path problems

### João Doriguello, National University of Singapore

In this work we study two problems: high-dimensional linear regression with an ℓ1- penalty (Lasso path problem) and clustering of large datasets (k-means problem). On one hand, while classical algorithms are available for Lasso, our focus is on developing a quantum algorithm that offers new insights and speedup. Quadratic speedup is possible over the classical Homotopy (Least Angle Regression) method. In particular, we provide a general setup for Lasso solutions as the penalty term varies. On the other hand, one of the most popular clustering algorithms is Lloyd’s iteration for k-means. This iteration takes N vectors and outputs k centroids; these partition the vectors into clusters based on which centroid is closest to a particular vector. We present an overall improved version of the “q-means” algorithm, the quantum algorithm originally proposed by Kerenidis, Landman, Luongo, and Prakash which is an approximate version of k-means clustering.

## A nonlocal game involving quantum graphs

### Priyanga Ganesan, University of California, San Diego

In this talk, we will explore the interaction between operator algebras and quantum information theory through a discussion on quantum graphs. Quantum graphs are an operator generalization of classical graphs that have appeared in different branches of mathematics including operator algebras, non-commutative topology, operator systems theory and quantum information theory. In this talk, I will give an introduction to the different perspectives to quantum graphs and their connections to quantum information. I will present a generalization of the nonlocal graph coloring game to the setting of quantum graphs, using a quantum-input classical-output nonlocal game. We will witness quantum supremacy by showing that every quantum graph has a finite quantum chromatic number, but not necessarily a finite classical chromatic number.

This is based on joint work with Michael Brannan and Samuel Harris.

## Classical simulation of non-Gaussian fermionic circuits

**Beatriz Dias ^{1,2}** and Robert König

^{1,2}

^{1}Department of Mathematics, School of Computation, Information and Technology, Technical University of Munich, Garching, Germany

^{2}Munich Center for Quantum Science and Technology, Munich, Germany

We propose efficient algorithms for classically simulating fermionic linear optics operations applied to non-Gaussian initial states. By gadget constructions, this provides algorithms for fermionic linear optics with non-Gaussian operations. We argue that this problem is analogous to that of simulating Clifford circuits with nonstabilizer initial states: Algorithms for the latter problem immediately translate to the fermionic setting. Our construction is based on an extension of the covariance matrix formalism which permits to efficiently track relative phases in superpositions of Gaussian states. It yields simulation algorithms with polynomial complexity in the number of fermions, the desired accuracy, and certain quantities capturing the degree of non-Gaussianity of the initial state. We study one such quantity, the fermionic Gaussian extent, and show that it is multiplicative on tensor products when the so-called fermionic Gaussian fidelity is. We establish this property for the tensor product of two arbitrary pure states of four fermions with positive parity.

## “Quantum Biology”: how nature harnesses quantum processes to function optimally, and how might we control such quantum processes to therapeutic advantage

### Plenary: Clarice Aiello, University of California, Los Angeles

Imagine driving cell activities to treat injuries and disease simply by using tailored magnetic fields. Many relevant physiological processes, such as: the regulation of reactive oxygen species; epigenetic changes to induce pluripotency; cell proliferation and wound healing; cellular respiration rates; ion channel functioning; and DNA repair were all demonstrated to be controlled by weak magnetic fields (with a strength on the order of that produced by your cell phone), very likely via the electron quantum property of “spin”. Research has not been able to track spin states to manipulate physiological outcomes in vivo and in real time, without which the potential game-changing clinical benefits of “Quantum Biology” cannot be realized. **With novel quantum instrumentation, we are learning to control spin states in cells and tissues, having as a goal to write the “codebook” on how to deterministically alter physiology with weak magnetic fields to therapeutic advantage**. In the long-term, the electromagnetic fine-tuning of endogenous “quantum knobs” existing in nature will enable the development of drugs and therapeutic devices that could heal the human body — in a way that is non-invasive, remotely actuated, and easily accessible by anyone with a mobile phone.

## The signal and the noise: learning with random quantum circuits and other agents of chaos

### Yihui Quek, Massachusetts Institute of Technology

What can we quantum-learn in the age of noisy quantum computation? Both more and less than you think. Noise limits our ability to error-mitigate, a term that refers to near-term schemes where errors that arise in a quantum computation are dealt with in classical pre-processing. I present a unifying framework for error mitigation and an analysis that strongly limits the degree to which quantum noise can be effectively `undone' for larger system sizes, and shows that current error mitigation schemes are more or less as good as they can be. After presenting this negative result, I'll switch to discussing how noise can be a friendly foe: non-unital noise, unlike its unital counterparts, surprisingly results in absence of barren plateaus in quantum machine learning.

## Fault-tolerant quantum computing beyond the surface code

### Michael Vasmer, Perimeter Institute

The surface code has for 20 years been the gold standard for building a fault-tolerant quantum computer. However, it suffers from one major drawback: a low encoding rate, which means that approximately 1000 physical qubits and 30 rounds of error correction are required to encode a logical qubit with adequate protection. In this talk we give an overview of the alternatives to the surface code, focusing on two code families in particular: 3D subsystem codes and hypergraph product codes. These alternative code families may offer lower overheads than the surface code, and could yet displace it as the leading candidate for building a fault-tolerant quantum computer.

## Quasiprobability simulation for near-term quantum computing

### Christophe Piveteau, ETH Zürich

Quasiprobability simulation is a technique that allows a quantum computer to simulate the execution of operations which are not physically realizable on said hardware. The technique entails an additional sampling overhead which scales exponentially in the number of non-physical gates that are simulated. In recent years, quasiprobability simulation has found many applications such as classical simulation of near-Clifford quantum circuits and error mitigation. Another such application is circuit cutting, i.e. the task of simulating non-local quantum computation between two parties with only local operations. In this talk, I will give an overview of these applications as well as recent work on characterizing the optimal achievable sampling overhead for circuit cutting, which interestingly has connections with the resource theory of entanglement. We also observe that in some settings there is a provable advantage when classical communication between the two parties is allowed during the circuit execution. Finally, we discuss some possible applications for near-term quantum computing.

## Bound states in photonic and atomic crystals

### Plenary: Alexey Gorshkov, National Institute of Standards and Technology and University of Maryland

First, we will discuss ultrastrong coupling between a fluxonium qubit and a one-dimensional photonic crystal [1]. We will show, both theoretically and experimentally, that the transport of a single photon in this regime is strongly modified by the presence of multi-photon bound states.

Second, we will report on the experimental realization of one-dimensional anyons using ultracold bosonic atoms in an optical lattice with a density-dependent hopping phase [2]. We will show that qualitative features of transport in this system can be understood in terms of the dispersion of two-atom bound states.

Third, if time permits, we will briefly present an unrelated project: we will show both theoretically and experimentally that, for the same level of noise, the so-called erasure noise (such as atom loss in an atomic clock) is less harmful to sensors and clocks than non-erasure noise (such as qubit dephasing) [3].

[1] Vrajitoarea, A., Belyansky, R., Lundgren, R., Whitsitt, S., Gorshkov, A. V., and Houck, A. A. Ultrastrong light-matter interaction in a photonic crystal. arXiv:2209.14972 (2022).

[2] Kwan, J., Segura, P., Li, Y., Kim, S., Gorshkov, A. V., Eckardt, A., Bakkali-Hassani, B., and Greiner, M. Realization of 1D Anyons with Arbitrary Statistical Phase. arXiv:2306.01737 (2023).

[3] Niroula, P., Dolde, J., Zheng, X., Bringewatt, J., Ehrenberg, A., Cox, K. C., Thompson, J., Gullans, M. J., Kolkowitz, S., and Gorshkov, A. V. Quantum Sensing with Erasure Qubits. arXiv.2310.01512 (2023).

## A dual-species Rydberg array

### Conor Bradley, University of Chicago

Optical tweezer arrays of neutral atoms have emerged as a powerful platform for quantum science, readily scaling to hundreds of qubits arranged in programmable geometries. I will present progress on the realization of a dual-element Rydberg array of rubidium and cesium atoms. This two-species architecture offers novel capabilities such as mid-circuit measurements, in-sequence reloading of atomic qubits, and unexplored interaction regimes. I will first discuss recent work on ‘spectator qubits’ in which we leveraged mid-circuit measurement and real-time feed-forward to correct correlated errors on a 2D array of up to 120 qubits [1]. I will then present preliminary results on implementing Rydberg interactions in this system, the key ingredient for universal quantum information processing and manybody quantum simulation.

[1] K. Singh*, C. E. Bradley*, S. Anand* et al., Mid-circuit correction of correlated phase errors using an array of spectator qubits, Science (2023)

## Progress towards quantum error correction with a programmable Rydberg array in an optical cavity

### Josiah Sinclair, Massachusetts Institute of Technology

It has been recently shown that surface code error-corrected qubits can be connected with noisy links without requiring distillation, better local gates, or space-time overheads [1]. Combining recent advances in atom arrays with these results I will report progress towards a flexible experimental platform for modular quantum computing comprising a programmable Rydberg atom array interfaced with an optical cavity. In such a platform, fault-tolerant scaling via noisy photonic interconnects can be achieved with two-qubit gate and Bell pair error thresholds of 1% and 10% respectively, as well as sufficiently fast entanglement distribution. I will also describe progress towards the nearer-term goal of using the cavity for scalable syndrome readout for quantum error correction.

## Observation of a finite-energy phase transition in a one-dimensional quantum simulator

### Alexander Schuckert, Joint Quantum Institute, University of Maryland

One of the most striking many-body phenomena in nature is the sudden change of macroscopic properties as the temperature or energy reaches a critical value. Such equilibrium transitions have been predicted and observed in two and three spatial dimensions, but have long been thought not to exist in one-dimensional (1D) systems. Fifty years ago, Dyson and Thouless pointed out that a phase transition in 1D can occur in the presence of long-range interactions, but an experimental realization has so far not been achieved due to the requirement to both prepare equilibrium states and realize sufficiently long-range interactions. Here we report on the first experimental demonstration of a finite-energy phase transition in 1D. We use the simple observation that finite-energy states can be prepared by time-evolving product initial states and letting them thermalize under the dynamics of a many-body Hamiltonian.By preparing initial states with different energies in a 1D trapped-ion quantum simulator, we study the finite-energy phase diagram of a long-range interacting quantum system. We observe a ferromagnetic equilibrium phase transition as well as a crossover from a low-energy polarized paramagnet to a high-energy unpolarized paramagnet in a system of up to 23 spins, in excellent agreement with numerical simulations.Our work demonstrates the ability of spin quantum simulators to realize and study previously inaccessible phases at finite energy density.

## Towards Quasi-Dual Species Operation with Metastable- and Ground-State Qubits in Barium

### Susanna Todaro, Oxford Ionics

Most quantum information experiments with trapped ions encode the qubit either between two Zeeman or hyperfine sublevels of the ground electronic state or between the ground state and a long-lived metastable state. A third category is the metastable qubit, in which quantum information is encoded in sublevels of the metastable state. Qubits in this manifold are largely insensitive to scattered laser light addressing a neighbouring qubit in the ground state manifold, since this light is far off-resonant. This enables quasi dual-species operation in a chain of identical ions, where a ground state qubit can potentially act as a sympathetic coolant or ancilla qubit to a neighbouring metastable qubit. Barium ions have accessible visible and infrared transition wavelengths and a metastable state with a 30 second lifetime, making them appealing for this application. Further, the three barium isotopes with nuclear spin* I* = 1/2 or 3/2 have hyperfine structure, enabling long-coherence time qubit encoding. To investigate this architecture, it is necessary to develop a toolbox of operations for simultaneous independent control of these two manifolds. I will present work towards a full toolbox for ground-state qubit operations in this architecture, focusing on (1) loading barium qubits into scalable surface-electrode traps and (2) implementing dissipative operations on a ground state qubit with no path through the metastable qubit manifold. This provides a path towards a quantum register of identical barium ions in which ions can be dynamically shifted between ground-state (coolant) and metastable (logic) manifolds. The research presented was performed at MIT and MIT-Lincoln Laboratory as a post-doctoral fellow; my current affiliation is Oxford Ionics.

## Quantum network based on color centers in diamond nanocavities

### Aziza Suleymanzade, Harvard University

Silicon Vacancy color centers in diamond, coupled to nanophotonic crystal cavities, offer a promising platform for quantum network applications. Our system utilizes long qubit coherence times, high optical cooperativities, and on-chip scalability, providing a unique path toward the practical implementation of long-distance quantum networking. In this talk, I will present our recent results on distributing entanglement across a two-node network we built at Harvard. We demonstrated high-fidelity entanglement between communication and memory qubits and showed long-distance entanglement over the 35 km of deployed fiber in the Cambridge/Boston area. I will also review our ongoing projects, including the realization of blind delegated computing and applications for long-baseline entangled telescopes using our platform.

## Reprogrammable integrated photonic circuits for quantum optics

### Tatsuhiro Onodera, NTT Research and Cornell University

Integrated photonics is a promising platform for quantum computing and sensing, but faces several key challenges, including the generation of large quantum states of light, and realizing low-loss interactions between many modes. In this talk, I will introduce our recent work on developing a programmable integrated photonics platform that is well-suited to tackle these challenges. Using the electro-optic effect in a Lithium Niobate planar waveguide and a photoconductive film, we develop a fully programmable planar waveguide, capable of in-situ, real-time modification of its spatial refractive index distribution n(x,z). In our initial work focused on classical photonic applications, we demonstrated reconfigurable photonic devices and performed machine learning classification of image and vowel datasets. I will discuss ongoing efforts to extend and apply this platform for quantum photonic applications, both for the programmable generation of complex multimode quantum states of light and for realizing large-scale programmable unitary operations.

## Spin squeezing-enhanced stability in an optical lattice clock comparison at the 10^{-17} level

### Maya Miklos, JILA, University of Colorado Boulder

Optical atomic clocks are advancing quantum metrology across many applications, from tests of fundamental symmetries to resolving the gravitational redshift on ever-shorter length scales [1, 2]. However, state-of-the-art optical atomic clock comparisons are approaching a fundamental noise floor set by the spin statistics of uncorrelated particles, known as the quantum projection noise (QPN) limit [3]. Leveraging entanglement of the atomic ensemble, in the form of spin squeezing, can allow us to surpass this limit and advance towards the ultimate stability bound set by the Heisenberg uncertainty principle. Realizing such spin-squeezing in a state-of-the-art clock is technically challenging, however, as it requires both a mechanism to generate many body interactions and precise control of an ultrastable optical local oscillator. We have constructed a hybrid platform with a strontium optical lattice clock operated together with an in-vacuum high-finesse optical cavity, to generate spin squeezing on the optical clock transition via cavity-mediated quantum non-demolition (QND) measurements of the collective spin-state. A conveyor-belt optical lattice is used to shuttle independent sub-ensembles in and out of the cavity to conduct a clock comparison between two independently spin-squeezed atomic ensembles that averages down to the 10^{-17} fractional frequency level [4]. This result represents a major step towards tackling the technical challenges needed to make spin squeezing practically useful to state-of-the-art atomic clocks.

1. C. Sanner et al., Nature 567, 204-208 (2019)

2. T. Bothwell et al., Nature 602, 420-424 (2022)

3. E. Oelker et al., Nature Photonics 13, 714-719 (2019)

4. J. M. Robinson et al., arXiv:2211.08621 (2023). Nature Physics, in press (2023).

## Dipolar interactions in a molecular tweezer array

### Annie Jihyun Park, Harvard University

Ultracold molecules offer rich internal states and tunable long-range interactions, making them favorable for a wide range of quantum science applications. I will discuss our platform of molecular qubits, where optical tweezer arrays of NaCs molecules are created by adiabatically assembling their constituent atoms. In our system, we protect the rotational coherence from trap-induced light shifts, the dominant source of decoherence, by rotating the tweezer polarization to a specific magic ellipticity. This technique allows us to encode a qubit in a pair of specific rotational levels with a coherence time of up to 250 ms. With coherence under control and leveraging the large dipole moment of NaCs, we observe a dipolar interaction strength of ~kHz between adjacent molecules, setting the stage for exciting opportunities in quantum computing and quantum simulation on our platform.

## Metamaterial Perfect Absorbers for Sensitive Avalanche Photodiodes in SWIR Region

### Sasan V. Grayli, Institute for Quantum Computing

The remarkable functionality of all-dielectric metamaterials in controlling of the light-matter interaction at nanoscale have led to creation of flat optics, near-zero index waveguides and directional scatterers. Enhanced absorption has also been demonstrated with all semiconductor metamaterials which is a desired attribute for improving the efficiency of solar cells as well as realizing low-light sensitive detectors. A known shortcoming of current commercial avalanche photodiodes (APD) is detection efficiency in the wavelength band from 850 nm – 1000 nm, known as the valley of death, a region of particular importance for biomedical applications including optical coherence tomography which can benefit from the improved selectivity gained from the incorporation of metamaterial absorbers. Here, we demonstrate that the enhanced absorption, that was achieved with the help of InGaAs semiconductor nanowire metamaterials, increases the overall efficiency of a detector. Our InGaAs nanowire metamaterial perfect absorber shows a very high responsivity in the valley of death which is a significant improvement to the commercially available APDs.

## Metasurface structures for control of quantum emitters

### Behrooz Semnani, Institute for Quantum Computing

In recent years, there has been a notable increase in research on diffractive optics, facilitated by advancements in nanofabrication techniques. The fabrication of large-area arrays of metallic and dielectric nanostructures with high precision and throughput has become feasible, leading to the introduction of new categories of diffractive optical structures. These developments have given rise to a new field known as flat optics, featuring key components called metasurfaces. Concurrently, Integrated Fabry-Perot cavities operating in free space have proven to be excellent platforms for enhancing light-matter interaction in various media, such as cold atoms and optically trapped single quantum emitters. Despite the prevalence of theoretical and experimental studies on cavity quantum electrodynamics (QED) mediated by cold atoms, there remains a lack of experimental demonstrations of integrated confocal cavities with accessible mode distribution in free space. In this context, we demonstrate how metasurface-assisted cavity structures can be employed to construct integrated Fabry-Perot cavities with a polarization degree of freedom. We also discuss the application of machine learning in inverse design to optimize flat optical structures suitable for quantum optics in atomic and solid-state platforms.

## Biographies

### Clarice Aiello, University of California, Los Angeles

Prof. Clarice D. Aiello is a quantum engineer interested in how quantum physics informs biology at the nanoscale. She is an expert on nanosensors harnessing room-temperature quantum effects in noisy environments. Aiello received her B.S. in Physics from the École Polytechnique; her M.Phil. in Physics from the University of Cambridge, Trinity College; and her Ph.D. from MIT in Electrical Engineering. She also held postdoctoral appointments in Bioengineering at Stanford, and in Chemistry at Berkeley. Two months before the pandemic, she joined UCLA, where she leads the Quantum Biology Tech (QuBiT) Lab.

### Harriet Apel, University College London

I am a PhD candidate in the computer science department at UCL, under the supervision of Prof. Toby Cubitt. My research has focused on the application and development of techniques from Hamiltonian complexity. So far I have applied these tools to tensor network models of holography and quantum error correction codes with constrained geometry.

I studied Physics at the University of Cambridge before returning to London for my Ph.D. Currently, I am based in San Francisco, interning at PsiQuantum in their algorithms and applications team.

### James Bartusek, University of California, Berkeley

James Bartusek is a PhD student at Berkeley, where he is advised by Sanjam Garg. He is interested in the foundations of cryptography, the peculiarities of quantum information, and in particular their interplay. Previously, he received a BSE and MSE from Princeton, where he was advised by Mark Zhandry.

### Paula Belzig, University of Copenhagen

Paula Belzig recently obtained a PhD from the University of Copenhagen and will join IQC at the University of Waterloo as a postdoctoral researcher from November 2023. Her research focuses on the theory of quantum communication with and without entanglement, and with and without noise assumptions on the communication setup. She is also more broadly interested in quantum computing, quantum cryptography and quantum error correction.

### Vjosa Blakaj, Technical University of Munich

Vjosa Blakaj is a Ph.D. student at the Technical University of Munich, advised by Michael M. Wolf. Her research has focused on developing a toolbox for addressing problems in quantum information theory and beyond, by combining tools from real algebraic geometry, transcendental number theory, differential geometry, and operator theory. She is a recipient of the IMPRS-QST (International Max-Planck Research School for Quantum Science and Technology) fellowship at the Max-Planck Institute of Quantum Optics. She holds B.Sc. and M.Sc. degrees in Mathematics from the University of Prishtina and the Technical University of Munich, respectively.

### Conor Bradley, University of Chicago

Conor Bradley is a Quantum Fellow at the University of Chicago, where he works in the Bernien Lab. His research aims to leverage the novel features of a dual-species array of Rydberg atoms for both quantum simulation and information processing. Prior to moving to Chicago, Conor completed his PhD in the Taminiau Lab at TUDelft, studying systems of nuclear spins coupled to NV centers in diamond. Highlights of his PhD work included the realization of the largest qubit register of solid-state spins and the observation of a many-body-localized discrete time crystal.

### Matthias C. Caro, Freie Universität Berlin

Matthias C. Caro is a postdoctoral researcher at Free University Berlin. Before returning to Berlin, he was a postdoctoral visiting research fellow at Caltech. His research lies at the intersection of quantum information theory and machine learning theory, contributing to a rigorous understanding of the potential and limitations of quantum machine learning. He completed his PhD under the supervision of Michael M. Wolf at the Technical University of Munich, where he worked mainly on statistical properties of variational quantum machine learning models.

### Beatriz Dias, Technical University of Munich

Beatriz Dias is a doctoral student at the Technische Universität München, in Germany, under the supervision of Prof. Robert König. She is interested in quantum information processing, namely in classically simulating quantum devices. Before starting her PhD, Dias completed her BSc and MSc in Physics at Instituto Superior Técnico in Lisbon, Portugal, after which she held a research scholarship at the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany.

### João Doriguello, National University of Singapore

João Doriguello is currently a postdoctoral researcher at the Centre for Quantum Technologies in the National University of Singapore working with Prof. Miklos Santha. Previously he completed his PhD at the University of Bristol from 2016 to 2021 under the supervision of Prof. Ashley Montanaro. His main research interests are communication complexity, query complexity, Boolean analysis, quantum algorithms and quantum finance.

### Priyanga Ganesan, University of California, San Diego

Dr. Priyanga Ganesan is currently employed as a UC President’s Postdoctoral Fellow at the University of California, San Diego. She received her PhD from Texas A&M University, College Station in May 2022.

Priyanga Ganesan’s research explores the connection between operator algebras and quantum information theory. Currently, her research focuses on quantum graphs and nonlocal games, the former providing quantum analogues for confusability graphs associated to classical communication channels and the latter providing mathematical thought experiments which witness non-trivial quantum entanglement. Quantum graphs and nonlocal games have their roots in operator algebras, and her research primarily deals with the transfer of properties and results between quantum information and the setting of C*-algebras.

### Alexey Gorshkov, National Institute of Standards and Technology and University of Maryland

Alexey Gorshkov received his A.B. and Ph.D. degrees from Harvard in 2004 and 2010, respectively. In 2013, after three years as a Lee A. DuBridge Postdoctoral Scholar at Caltech, he became a staff physicist at NIST. At the same time, he started his own research group at the University of Maryland, where he is a fellow of the Joint Quantum Institute and of the Joint Center for Quantum Information and Computer Science. His theoretical research is at the interface of quantum optics, atomic physics, condensed matter physics, and quantum information science. Applications of his research include quantum computing, quantum communication, and quantum sensing. He is a recipient of the 2022 Optica Fellowship, the 2023 Samuel Wesley Stratton Award, the 2020 Arthur S. Flemming Award, the 2020 APS Fellowship, the 2019 PECASE, and the 2018 IUPAP Young Scientist Prize in AMO Physics.

### Sasan V. Grayli, Institute for Quantum Computing

Sasan V. Grayli is a scientist/entrepreneur with a strong background in plasmonics and nanophotonics, and an extensive hands-on experience in nanofabrication and electrochemistry. His doctoral work has led to fist in the world demonstration of highly controllable epitaxial growth of single-crystal gold film at wafer scale, with help of a simple electrochemical process. Furthermore, Sasan showed the advantage of this approach in fabrication of single crystal plasmonic metasurfaces on both metallic and dielectric substrates. He continued his work by demonstrating the deposition of other noble metals and their alloys with monocrystalline quality. Sasan is currently a postdoctoral researcher at the University of Waterloo Institute for Quantum Computing. His current research is focused on integrated quantum nanophotonic devices and the realization of single-photon detectors, with the help of dielectric metamaterials, that are operational at room temperature environments. Sasan’s main research interests are in plasmonics, hot-electron devices for energy harvesting, quantum nanophotonics, metasurfaces and metamaterials. His practical approach to science has awarded him with 4 patents in the areas of photonic storage devices and materials science. Sasan has coauthored several journal papers and 2 book chapters.

### Jiahui Liu, Massachusetts Institute of Technology

Jiahui Liu is a postdoctoral researcher at Massachusetts Institute of Technology. She recently obtained her PhD degree in computer science from the University of Texas at Austin. Her research interests are in the intersection of quantum computing and cryptography

### Fermi Ma, Simons Institute and UC Berkley

Fermi Ma is a Simons-Berkeley postdoctoral fellow hosted by Umesh Vazirani. He received his PhD in 2021 from Princeton, where he was advised by Mark Zhandry. His research studies the relationship between quantum computation and the foundations of cryptography.

### Maya Miklos, JILA, University of Colorado Boulder

Maya Miklos is a graduate student in Jun Ye’s group at JILA in Boulder, Colorado, where she and her teammates have constructed and are characterizing a hybrid strontium atomic clock-cavity QED system. This platform is ideal for realizing spin squeezing-enhanced clock performance at state-of-the-art stability levels, and also offers the ability to probe cavity-mediated many-body dynamics with the exquisite sensitivity of an atomic clock. She previously received a B.A. in physics and math and concurrent M.A. in physics from Harvard, where she worked in Mikhail Lukin’s group on a project coupling nitrogen vacancy centers in diamond to nanomechanical resonators.

### Annie Jihyun Park, Harvard University

I am a postdoctoral researcher in Professor Kang-Kuen Ni's group at Harvard University. My research focuses on controlling ultracold polar molecules trapped in optical tweezers for quantum simulation and computation. Prior to joining the Ni group, I built a quantum simulator based on ultracold strontium atoms as a part of my PhD work in Professor Immanuel Bloch's group at the Max Planck Insitute of Quantum Optics.

### Christophe Piveteau, ETH Zürich

Christophe Piveteau received B.Sc. degrees in physics and mathematics and a M.Sc. degree in physics from ETH Zurich, Switzerland. During that time, he worked at IBM Research Zurich to develop algorithms for in-memory computing and deep learning acceleration with memristive crossbar arrays. Since 2020, he is pursuing a Ph.D. program in quantum information theory at ETH Zurich. His research interests include, among others, quantum error correction, quantum error mitigation, circuit cutting and machine learning.

### Tatsuhiro Onodera, NTT Research and Cornell University

Tatsuhiro is a post-doctoral research scientist with NTT Research’s PHI Laboratory, and Cornell University, where he works in the laboratory of Peter McMahon. He received his BASc in Engineering Science from the University of Toronto in 2014, and his PhD in Applied Physics, under the supervision of Hideo Mabuchi, from Stanford University in 2019. His research interests include nanophotonics, quantum optics, and the physics of computation.

### Yihui Quek, Massachusetts Institute of Technology

Yihui's interest in quantum was piqued after her senior thesis at MIT under the supervision of Peter Shor. After a scenic route through academia that wandered through biophysics, classical information theory and quantum Shannon theory during her PhD at Stanford under Tsachy Weissman, and a year in Berlin as a Humboldt fellow in the group of Jens Eisert, she now wants to lay the groundwork for a new kind of physical computer science – where physics influences the development of post-digital computing architectures and our understanding of what and how we can compute.

### Alexander Schuckert, Joint Quantum Institute, University of Maryland

Alex is a postdoctoral fellow at the Joint Quantum Institute. He thinks about how to use current digital and analogue quantum simulators to learn about many-body quantum systems, with the goal of moving closer toward comparing quantum simulation experiments with measurements on solids. Towards this goal, he has recently been working on how to measure finite temperature observables in quantum simulators. This work happens in very close collaboration with experiments, including digital quantum computers, ion trap simulators and ultracold gases.

### Josiah Sinclair, Massachusetts Institute of Technology

Josiah Sinclair is a postdoctoral associate in the Vuletić group at the MIT-Harvard Center for Ultracold Atoms where he researches quantum computing and quantum simulation on a programmable Rydberg array in an optical cavity. Josiah was born in Canada and received his B.S. in physics from Calvin College in 2013. He then continued his studies at the University of Toronto and graduated with his PhD in physics in 2021. Josiah’s research interests concern what we can discern about the ‘history’ of quantum particles, the harnessing of light-matter interaction and Rydberg blockade for the development of new quantum technologies, and quantum error correction and quantum computing.

### Aziza Suleymanzade, Harvard University

Aziza is a postdoc at Harvard in the group of Mikhail Lukin. She did her PhD at the University of Chicago in groups of Jon Simon and David Schuster, working on the transduction of single optical to millimeter wave photons using Rydberg atoms in cavities. Aziza got a Bachelor's degree from Harvard University and an MPhil from the University of Cambridge, where she built an experiment for generating potassium-39 BEC in a uniform box potential.

### Susanna Todaro, Oxford Ionics

Susanna Todaro received her Ph.D. in Physics in 2020 from the University of Colorado in Boulder, where she studied techniques for scaling up trapped-ion quantum computing systems in the Ion Storage Group at the National Institute of Standards and Technology. After graduating, she joined the joint group of Isaac Chuang and John Chiaverini at the Massachusetts Institute of Technology and MIT-Lincoln Laboratory as a postdoctoral fellow, investigating novel qubit encodings in trapped ion systems. She recently began a position at Oxford Ionics as a senior quantum scientist, where she is applying her experience with trapped-ion systems to help develop a large-scale commercial trapped-ion quantum computer.

### Michael Vasmer, Perimeter Institute

Michael grew up in the UK, where he did his university studies. He gained a Masters of Science degree at Durham University, studying Physics and Computer Science. He then went on to study at University College London, where he began working in quantum information science. He completed his PhD under the supervision of Dan Browne, with a thesis on quantum error correction. After graduating in 2019, Michael was a postdoc at Perimeter Institute and Institute for Quantum Computing in Waterloo, where he continued his research into fault-tolerant quantum information processing. He currently splits his time between working as a research scientist at Perimeter Institute / IQC and a senior quantum architecture scientist at Xanadu Quantum Technologies.

### Freek Witteveen, University of Copenhagen

I am Freek Witteveen, currently a postdoc at QMATH in Copenhagen. Before that, I did my PhD at QuSoft and the University of Amsterdam with prof. Michael Walter. My research interests are broadly at the interface of many-body physics and quantum information sciences, in particular mathematical aspects of tensor networks.