**Monday, September 30, 2019
Lazaridis QNC 0101**

8:30 am | Registration |

9:00 am | Welcoming remarks |

9:10 am |
Lindsay LeBlanc, University of Alberta |

10:10 am |
Aurelia Chenu, Donostia International Physics Center |

10:55 am | Coffee break |

11:15 am |
Rahul Trivedi, Stanford University (Vuckovic group) |

12:00 pm |
Carlos Antón-Solanas, Centre de Nanosciences et de Nanotechnologies (Senellart group) |

12:45 pm | Lunch |

1:30 pm |
Logan Clark, University of Chicago (Simon group) |

2:15 pm |
Wenchao Xu, Massachusetts Institute of Technology (Vuletic group) |

3:00 pm | Group photo and coffee break |

3:25 pm |
Peter McMahon, Cornell University |

4:25 pm |
Adolfo del Campo, Donostia International Physics Center |

5:15 pm | Reception with IQC faculty in Lazaridis QNC 2101 |

6:15 pm | Lazaridis QNC lab tours |

8:15 pm | Guided tour of Uptown Waterloo |

**Tuesday, October 1, 2019
Research Advancement Centre (RAC) 1, Room 2009**

9:00 am |
Diana Prado Lopes Aude Craik, Harvard University (Walsworth & Hu groups) |

9:45 am |
Brendan Shields, University of Basel (Maletinsky group) |

10:30 am | Coffee break |

10:50 am |
Sara Campbell, University of California, Berkeley (Muller group) |

11:35 am |
Hari Nair, Cornell University (Schlom group) |

12:20 pm | Lunch |

1:00 pm | Career panel discussion (G. Campbell, L. LeBlanc, P. McMahon) |

2:30 pm | Coffee break |

2:50 pm | Martin Sandberg, IBM Plenary talk: Superconducting quantum circuits as a path for quantum computing |

3:50 pm | Zlatko Minev, IBM and Yale University (Devoret group) To catch and reverse a quantum jump mid-flight |

4:40 pm | RAC 2 lab tours |

6:50 pm | BBQ |

9:00 pm | End of day |

**Wednesday, October 2, 2019
Lazaridis QNC 0101**

9:00 am | Gretchen Campbell, Joint Quantum Institute, NIST and UMD College Park Plenary talk: A Supersonically expanding BEC: An expanding universe in the lab |

10:00 am |
Brynle Barrett, iXblue |

10:45 am | Coffee break |

11:05 am |
Crystal Noel, Joint Quantum Institute, University of Maryland (Monroe group) |

11:50 am |
Sara Mouradian, University of California, Berkeley (Haeffner group) |

12:35 pm | Lunch |

1:35 pm |
Christian Kraglund Anderson, ETH Zürich (Wallraff group) |

2:20 pm |
Chiao-Hsuan Wang, University of Chicago (Jiang group) |

3:00 pm | Coffee break |

3:30 pm | Christie Chiu, Princeton University (Houck group) Microscopic studies of the doped Hubbard model |

4:15 pm | Adèle Hilico, Laboratory for Photonics, Numbers and Nanosciences - OLGS (Institute of Optics Graduate School) / CRNS / University of Bordeaux Ultra-cold atoms in a nano-structured optical lattice |

5:00 pm | Free time |

6:15 pm | Banquet dinner at the University Club |

9:00 PM | End of day |

**Thursday, October 3, 2019****Lazaridis QNC 0101**

9:00 am | Alexandre Cooper-Roy, University of Waterloo Plenary talk: An atomic array optical clock with single-atom readout |

10:00 am |
Ahmed Omran, Harvard University (Lukin group) |

10:45 am | Break |

11:05 am |
Aziza Suleymanzade, University of Chicago (Simon & Schuster groups) |

11:50 am |
Boris Braverman, University of Ottawa (Boyd group) |

12:50 pm | Closing remarks |

1:00 pm | Lunch |

## Abstracts

**Lindsay LeBlanc, University of Alberta **

Plenary talk: Optical Autler-Townes quantum memory in ultracold atomic ensembles

The ability to store and manipulate quantum information encoded in electromagnetic (often optical) signals represents one of the key tasks for quantum communications and computation schemes. In the pursuit of a practical but efficient and broadband quantum memory, we make use of a three-level atomic system (in our case, laser-cooled rubidium atoms) and realize storage and photonic manipu- lations in the regime of Autler-Townes splitting (ATS), where a classical-level control field controls the absorption of an auxillary, possibly quantum, signal field. We demonstrate on-demand storage and retrieval of both high-power and less-than-one-photon optical signals with total efficiencies up to 30%, using the ground state spin-wave as our storage states. Recently, we began storing signals in much colder samples, approaching the transition to Bose-Einstein condensation. We also realize a number of photonic manipulations, including temporal beamsplitting, frequency conversion, and pulse shaping. The ATS memory scheme is inherently fast and broadband, and, in contrast to the related schemes, is less demanding in terms of technical resources, making it a leading candidate for practical quantum technologies.

**Aurelia Chenu, Donostia International Physics Center**

Quantum thermodynamics and superadiabatic control of complex systems

Quantum thermodynamics is an emerging field with potential application to nanoscience. At the quantum level, work becomes a stochastic variable, and the work probability distribution is key to characterize a working medium. Complex quantum systems can boost the performance of quantum machines, but their characterization is challenging due to a complexity exponentially scaling with the system size. I will present a characterization of work in driven chaotic quantum systems, which are paradigmatic complex systems, using theory of random matrix Hamiltonians. Specifically, I will discuss the work statistics associated with a sudden quench for arbitrary temperature and system size [1]. In addition, I shall show how work statistics can generally be related to a dynamical problem: the evolution of quantum correlations of an entangled state [2]. Using this mapping, it is possible to connect work statistics to information scrambling, i.e., the spreading of initially localized quantum information across different degrees of freedom in many-body systems, which is a key quantity in the study of quantum chaos.

In a second part, I shall focus on control schemes to fasten the dynamics of the thermodynamic strokes of a quantum engine. Using shortcuts to adiabaticity, I demonstrate the improvement of the output power in compression and expansion strokes, with experimental implementation in a unitary Fermi gas [3]. This superadiabatic control scheme can be extended to open system [4], making possible the fast thermalization of a quantum system.

References:

[1] A. Chenu, J. Molina-Vilaplana, A. del Campo, Quantum 3:127 (2019)

[2] A. Chenu, I. Egusquiza, J. Molina-Vilaplana, A. del Campo, Sci. Rep. 8:12634 (2018) [3] S. Deng, A. Chenu, P. Diao, F. Li, S. Yu, I. Coulamy, A. del Campo, and H. Wu, Science Adv. 4:5909 (2018)

[4] S. Alipour, A. Chenu, A. Rezakhani, and A. del Campo, arXiv:1907.07460

**Rahul Trivedi, Stanford University (Vuckovic group)**

Scattering theory in quantum optics

Scattering matrices have been a key theoretical tool for the analysis of quantum field theories. Quantum optics studies the interaction of optical fields, which can be described by a field theory, with low dimensional systems (such as quantum emitters, optical cavities etc.) which can be described by a finite-dimensional or countably infinite-dimensional Hilbert space. Such systems serve as building blocks of optics-based quantum information processing systems. In this talk, I will go over the connection between scattering matrices and the input-output formalism for time-dependent and time-independent Markovian quantum optical systems [1, 2], as well as their computation. I will show how the scattering matrix formalism can be used to understand the dynamics of some paradigmatic systems, such as driven two-level systems for single-photon generation [1, 2] and broadband linear optical devices [3]. Finally, I will apply this formalism to understanding photon-blockade in the Tavis-Cumming system with mesoscopic number of emitters (~50 emitters) [4]. I will show how scattering matrices can allow development of a hierarchy of approximations calculable in polynomial time in the system size for simulating the Tavis-Cumming system. This simulation method makes it possible to study the impact of number of emitters on the light scattered from the Tavis-Cumming system, revealing some previously unknown properties of resonant and detuned photon blockade through this system. Finally, I will provide an outlook on the application of scattering matrix formalism to studying non-Markovian quantum-optical systems, such as time-delayed feedback systems with possible applications to design of nearly all-optical quantum memories.

References:

[1] Rahul Trivedi, Kevin Fischer, Shanshan Xu, Shanhui Fan, and Jelena Vuckovic. “Few-photon scattering and emission from low-dimensional quantum systems.” Physical Review B 98, no. 14 (2018): 144112.

[2] Kevin Fischer, Rahul Trivedi, Vinay Ramesh, Irfan Siddiqui and Jelena Vuckovic. “Scattering into one-dimensional waveguides from a coherently-driven quantum-optical system.” Quantum 2, 69 (2018).

[3] Rahul Trivedi, Kevin Fischer, Sattwik Deb Mishra, and Jelena Vuckovic. “Point-coupling Hamiltonian for broadband linear optical devices.” arXiv:1907.02259 (2019).

[4] Rahul Trivedi, Marina Radulaski, Kevin A. Fischer, Shanhui Fan, and Jelena Vučković. “Photon Blockade in Weakly Driven Cavity Quantum Electrodynamics Systems with Many Emitters.” Physical Review Letters 122, no. 24 (2019): 243602.

**Carlos Antón-Solanas, Centre de Nanosciences et de Nanotechnologies (Senellart group)**

Generation of non-classical light in a photon-number superposition

The ability to generate light in a pure quantum superposition is central to the development of quantum- enhanced technologies such as distributed quantum computing, long distance quantum communications or quantum sensing. Light offers many degrees of freedom to encode the quantum information including polarization, frequency, time bin, orbital angular momentum among others, allowing for large encoding Hilbert spaces. While the photon-number basis is natural for discrete variable encoding, the generation of light in coherent superpositions in photon-numbers remains challenging. So far, this has mostly been demonstrated through quantum-state engineering via the interference between heralded single-photon sources and coherent light [1].

Here we show that a single semiconductor quantum dot in a cavity can directly generate quantum superpositions of zero, one, and two photons. We investigate devices consisting of a single semi-conductor quantum dot positioned with nanometre scale accuracy at the centre of a connected-pillar cavity [2,3]. The quantum dot layer is inserted in a p-i-n diode structure and electrical contacts are defined as to control the quantum dot optical resonance through the confined Stark effect. These devices show strong suppression of decoherence processes arising from charge noise or coupling to phonons. They generate highly indistinguishable single-photons with high extraction efficiency [4]. We coherently drive the quantum dot transition with short laser pulses and observe Rabi oscillations as a function of the laser pulse area. We perform interferometric measurements in a Mach-Zehnder interferometer (MZI) that evidence that the quantum dot emits a coherent superposition of vacuum, and one-photon in a well-defined propagating mode of the electromagnetic field. Below the π-pulse, the zero- and one-photon populations are controlled through the laser intensity and exhibit near to maximal quantum coherence [5].

Figure 1: The double oscillation of the simultaneous coincidences (bottom, red trace) with respect to the single counts (top, blue trace), detected at the output of a MZI, evidences that the light emitted from our QD-cavity device is in a superposition of Fock states 0, 1 and 2. (right) Corresponding Fock state populations.

Driving the quantum dot with a 2π-pulse produces coherent superpositions of vacuum, one and two photons where the 2-photon Fock state population is larger than the 1-photon population. This state shows phase super-resolution in interferometric measurements (see left panels of Fig. 1), where p2 ≈ 2p1, (right panel of Fig. 1), and it has a high fidelity to an even Schrödinger kitten state (with average photon number of 0.5) [5]. Our results demonstrate that quantum dot based artificial atoms are now controlled to such a degree that they can perform as text-book idealized systems. They open new paths for optical quantum technologies where generalized multi-photon interferences, including the photon-number degrees of freedom, can be exploited.

References:

[1] E. Bimbard et al, Nat. Photon. 4, 243 (2010), T. J.

[2] A. Dousse et al., Phys. Rev. Lett. 101, 267404

[3] A. Nowak et al, Nature Commun. 5, 3240 (2014). Bartley et al, Phys. Rev. A 86, 043820 (2012).

[4] N. Somaschi et al., Nature Photon. 10, 340 (2016).

[5] J. C. Loredo∗, C. Anton∗, et. al, arXiv:1810.05170(2008). (2018).

**Logan Clark, University of Chicago (Simon group)**

Building Laughlin puddles of light

Can strongly correlated materials be built out of light? Ordinary photons, which freely propagate at the speed of light and do not interact with each other at all, cannot form such materials. However, I will explain how we turn photons into strongly-interacting cavity Rydberg polaritons, quasiparticles which inherit their spatial waveforms from the modes of an optical cavity and gain strong interactions from Rydberg excitations of an atomic gas. These polaritons can indeed form quantum materials. In fact, we have recently observed the formation of photon pairs in the Laughlin state, the paradigmatic example of a topologically ordered state which underlies the fractional quantum Hall effect in electron gases. We characterize these Laughlin “puddles” by measuring photon-photon correlations in both real space and angular momentum space, exemplifying the unique and powerful new perspective that many-body quantum optical systems can provide for understanding quantum matter.

**Wenchao Xu, Massachusetts Institute of Technology (Vuletic group)**

Strongly interacting photons in a quantum nonlinear medium

Manipulating individual photons is fascinating for building up all-optical quantum devices. In addition, it opens the possibility to realize novel quantum many-body states made with photons. Photons interact weakly in vacuum. However, via the combination of electromagnetically induced transparency and Rydberg atoms, strong mutual interactions between photons are realized. In this talk, I will present our group’s work on the full-control of the effective interactions of individual photons. These interactions range from attraction, characterized by the formation of bound states of photons, to repulsive interactions, which leads to the observation of emergent spatial structure.

**Peter McMahon, Cornell University**

Plenary talk: A quantum annealer with fully programmable all-to-all coupling via Floquet engineering

Quantum annealing is a promising approach to heuristically solving difficult combinatorial optimization problems. However, the connectivity limitations in current devices lead to an exponential degradation of performance on general problems. We propose an architecture for a quantum annealer that achieves full connectivity and full programmability while using a number of physical resources only linear in the number of spins. We do so by application of carefully engineered periodic modulations of oscillator-based qubits, resulting in a Floquet Hamiltonian in which all the interactions are tunable; this flexibility comes at a cost of the coupling strengths between spins being smaller than they would be had the spins been directly coupled. Our proposal is well-suited to implementation with superconducting circuits, and we give analytical and numerical evidence that fully-connected, fully-programmable quantum annealers with 1000 qubits could be constructed with Josephson parametric oscillators having cavity-photon lifetimes of 100 microseconds, and other system-parameter values that are routinely achieved with current technology. Our approach could also have impact beyond quantum annealing, since it readily extends to bosonic quantum simulators and would allow the study of models with arbitrary connectivity between lattice sites.

Reference:

[1] T. Onodera*, E. Ng*, P.L. McMahon. arXiv:1907.05483

**Adolfo del Campo, Donostia International Physics Center**

Probing topological defect formation in a quantum annealer

When a quantum phase transition is crossed in finite time, the breakdown of adiabatic dynamics leads to the formation of topological defects. The average density of defects scales with the quench rate following a universal power-law predicted by the Kibble- Zurek mechanism. The later provides useful heuristics for adiabatic quantum computation.

Physics beyond the Kibble-Zurek mechanism can be probed by characterizing the full counting statistics of topological defects. We argue that the distribution of the number of defects generally follows a Poisson binomial distribution with all cumulants exhibiting a universal power-law scaling with the quench rate.

As an exampled, we report the exact kink number distribution in the transverse-field quantum Ising model. For this system, we test kink statistics in a D-Wave machine and show that the study of the kink number distribution can be used to benchmark the performance of a quantum processor.

References:

[1] A. del Campo, Phys. Rev. Lett. 121, 200601 (2018)

[2] Jin-Ming Cui, F. J. Gómez-Ruiz, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, A. del Campo, arXiv:1903.02145

[3] Y. Bando et al, in preparation

**Diana Prado Lopes Aude Craik, Harvard University (Walsworth & Hu groups)**

Using microwaves to study charge state in NV diamond

D. P. L. Aude Craik, P. Kehayias, A. S. Greenspon, X. Zhang, M. J. Turner, J. M. Schloss, E. Bauch, C. A. Hart, E. L. Hu, R. L. Walsworth

In its negatively-charged state, the nitrogen vacancy center in diamond (NV−) can be used as an optically-read-out spin sensor of nanoscale magnetic fields with exciting applications ranging from imaging fields in living cells to extracting information about the formation of our solar system from paleomagnetic early-Earth rocks. In contrast, the neutral charge state of the defect (NV0) offers no optical spin readout, producing only a spin-independent fluorescence background under the 532-nm illumination typically used to read out NV− ensembles. Hence, to maximize sensitivity of ensemble-based magnetometers, we would like to understand how to produce diamond samples in which the NVs are predominantly negatively charged.

I will present a novel, microwave-based technique for determining charge state of nitrogen- vacancy (NV) ensembles in diamond. The technique isolates, in situ, the spectral shape of the fluorescence contribution from neutral (NV0) and negatively-charged (NV−) defects, producing sample-specific results which take into account the effects of experimental conditions (such as illu- mination intensity and wavelength) and material properties (such as local strain and electric fields). Using this technique, we study the physics of NV ionization from the negative charge state, identi- fying previously unobserved ionization trends. Further, I will describe applications of the method to spectroscopy of other solid-state defects and to enhancement of magnetometry sensitivity.

**Brendan Shields, University of Basel (Maletinsky group)**

Imaging nanoscale antiferromagnetic order with a scanning nitrogen-vacancy microscope

The nitrogen-vacancy (NV) color center in diamond is an exceptional atomic- scale system with a coherent electronic spin degree of freedom that can be initialized and measured optically. These properties make the NV attractive for applications ranging from quantum information to nanoscale metrology. Here, we use the NV electronic spin as a quantum scanning magnetic field probe to quantitatively image antiferromagnetic order in a granular thin film of Cr_{2}O_{3} [1]. By incorporating a single NV into the tip of a monolithic diamond atomic force microscopy probe and monitoring the Zeeman shift of the NV ground state electron spin, we image the stray magnetic field of a 200-nm thick film of Cr_{2}O_{3} at nanoscale resolution, observing the formation of antiferromagnetic domains as the film transitions from paramagnetic to antiferromagnetic order. In combination with Zero-Offset Hall Magnetometry, we characterize key material properties of the Cr_{2}O_{3} sample, including local critical temperature and inter-granular exchange.

Reference:

[1] Patrick Appel, Brendan J. Shields et al., Nanomagnetism of magnetoelectric granular thin-film antiferromagnets, Nano Letters 19(3), 1682- 1687 (2019).

**Sara Campbell, University of California, Berkeley (Muller group)**

Laser-based phase contrast transmission electron microscopy

Laser-based preparation, manipulation, and readout of the states of quantum particles has become a powerful research tool that has enabled the most precise measurements of time, fundamental constants, and electromagnetic fields. Laser control of free electrons can improve the detection of electrons' interaction with material objects, thereby advancing the exploration of matter on the atomic scale. For example, temporal modulation of electron waves with light has enabled the study of transient processes with attosecond resolution. In contrast, laser-based spatial shaping of the electron wave function has not yet been realized, even though it could be harnessed to probe radiation-sensitive systems, such as biological macromolecules, at the standard quantum limit and beyond. Here, we demonstrate laser control of the spatial phase profile of the electron wave function and apply it to enhance the image contrast in transmission electron microscopy. We first realize an electron interferometer, using continuous-wave laser-induced retardation to coherently split the electron beam, and capture TEM images of the light wave. We then demonstrate Zernike phase contrast by using the laser beam to shift the phase of the electron wave scattered by a specimen relative to the unscattered wave. Laser-based Zernike phase contrast will advance TEM studies of protein structure, cell organization, and complex materials. The versatile coherent control of free electrons demonstrated here paves the way towards quantum-limited detection and new imaging modalities.

**Hari Nair, Cornell University (Schlom group)**

Demystifying the growth of superconducting Sr_{2}RuO_{4} thin films

Sr_{2}RuO_{4} is an unconventional superconductor with potentially a spin- triplet, odd-parity topologically nontrivial p_{x} ± ip_{y} superconducting ground state. There are many reports of high purity single crystals of Sr_{2}RuO_{4} with a Tc of up to 1.5 K. To date, however, there are only four published reports of superconducting Sr_{2}RuO_{4} thin films. The three others than ours have Tcs significantly below 1.5 K. This relative paucity of superconducting thin films is likely due to the extreme sensitivity of the odd-parity superconducting ground state in Sr_{2}RuO_{4} to disorder. Thin films provide a pathway for scalability, which is critical for potential practical applications of spin-triplet superconductors such as qubits for topological quantum computing. Here, we outline and demonstrate a thermodynamic growth window to achieve repeatable growth of superconducting Sr_{2}RuO_{4} with higher Tc, up to 1.8 K. This Tc is higher than all prior thin films and even higher than unstrained Sr_{2}RuO_{4} single crystals.

**Christie Chiu, Princeton University (Houck group)**

Microscopic studies of the doped Hubbard model

Ultracold fermions in optical lattices offer new perspectives for studying the physics of strongly correlated materials. In the group of Markus Greiner, we use this experimental platform to implement the Fermi-Hubbard model, a paradigmatic model thought to capture the physics of high-temperature superconductivity, the pseudogap, and other phenomena containing long- standing open questions. The additional tool of quantum gas microscopy enables site-resolved readout and access to projections of the many-body wavefunction in the Fock basis. I report on our recent studies of doped antiferromagnets in two dimensions, where there is no universally agreed-upon mechanism describing the interplay between hole motion and antiferromagnetic order.

**Adèle Hilico, Laboratory for Photonics, Numbers and Nanosciences - OLGS (Institute of Optics Graduate School) / CRNS / University of Bordeaux**

Ultra-cold atoms in a nano-structured optical lattice

Due to their number of controllable parameters, cold atoms in lattices have been used as quantum simulators. In the current state of the art, the experimental techniques use optical lattices in the far-field, limiting the lattice spacing to a half wavelength. Such large spacing limits the relevant energy scale (tunneling, interaction) which makes it difficult to enter deeply into magnetic quantum correlations regimes or strongly correlated phases. Our project aims at reducing the lattice period to bridge the gap between solid state (0.1 nm) and far field lattice (500 nm). For this we develop a hybrid quantum system of degenerate gaz in close proximity with a nano-structured surface generating sub-wavelength lattice potentials. In this presentation, I will discuss theoretical results on a novel trapping scheme to compensate the Casimir Polder force at very short distance and experimental evidences of a sub-wavelength imaging technic for cold atoms.

**Gretchen Campbell, Joint Quantum Institute, NIST and UMD College Park**

Plenary talk: A Supersonically expanding BEC: An expanding universe in the lab

The massive scale of the universe makes the experimental study of cosmological inflation difficult. This has led to an interest in developing analogous systems using table top experiments. One possible system for such simulations is an expanding atomic quantum gas. In recent experiments, we have modeled the basic features of an expanding universe by drawing parallels with an expanding ring-shaped Bose Einstein Condensate (BEC). The Bose- Einstein condensate can be thought of as a vacuum for phonons, and used in analogy to the quantum field proposed to have driven the expansion of the early universe. Here, while the ring-shaped BEC serves as the background vacuum, the phonons are the analogue to photons in the expanding universe. We have studied the dynamics of a supersonically expanding ring- shaped BEC both experimentally and theoretically. I will present our results and discuss prospects for future experiments.

**Brynle Barrett, iXblue **

Hybrid matter-wave inertial sensors for mobile sensing applications

B. Barrett^{1}^{,2,} P. Cheiney^{1}^{,2}, S. Templier^{1}^{,2}, B. Gouraud^{1}^{,2}, B. Battelier^{2}, H. Porte^{1}, F. Napolitano^{1}, and P. Bouyer^{2}

High-sensitivity, low-drift inertial sensors based on cold-atom interferometry are poised to revolutionize the field of inertial guidance and navigation, yet many challenges still remain. For instance, due to the slow data rate of atom interferometers and the large bias drifts of mechanical accelerometers, hybridization schemes will almost certainly be necessary [1,2,3]. We present recent results on the hybridization of classical and quantum accelerometers in a simulated navigation environment exhibiting strong variations in temperature and vibration noise. By correlating the output of each sensor, and utilizing a novel real-time system, we are able to lock the classical accelerometer to the quantum interference fringe [4]. This feedback loop simultaneously rejects motion-induced frequency and phase shifts on the quantum accelerometer, and corrects for bias drifts on the classical one—enabling us to achieve sub-micro-g precision after a few seconds of integration. This system paves the way toward a fully-hybridized multi-axis inertial measurement unit [5] compatible with mobile sensing applications.

Figure 1. Performance of our hybrid quantum accelerometer in a “noisy” environment. (a) Classical accelerometer bias as the temperature is varied over 4.5 hours. (b) Bias error signal from the hybrid accelerometer lock. (c) Allan deviation of the bias error. Hybrid sensor characteristics: interrogation time T = 20 ms, cycle time 1.2 s, bias sensitivity ∼ 1.6 μg/√Hz.

References:

[1] J. Lautier et al, Appl. Phys. Lett. 105, 144102 (2014).

[2] P. Cheiney et al, Phys. Rev. Applied 10, 034030 (2018).

[3] Y. Bidel et al, Nat. Commun. 9, 627 (2018).

[4] P. Cheiney et al, in Proc. of IEEE International Symposium on Inertial Sensors and Systems, Naples, USA (2019).

[5] B. Barrett et al, Phys. Rev. Lett. 122, 043604 (2019).

**Crystal Noel, Joint Quantum Institute, University of Maryland (Monroe group)**

C. Noel^{1} , L. Egan^{1} , A. Risinger^{1} , D. Zhu^{1} , M. Goldman^{1} , M. Cetina^{1} , C. Monroe^{1}^{1}Joint Quantum Institute Department of Physics, University of Maryland, College Park 20742

C. Noel^{2}^{} , M. Berlin-Udi^{2} , C. Matthiesen^{2} , J. Yu^{2} , Y. Zhou^{2} , V. Lordi^{3} , and H. Häffner^{2}^{2}Department of Physics, University of California, Berkeley, California 94720, USA^{3}Lawrence Livermore National Laboratory, Livermore, California 94551, USA

Under the IARPA LogiQ program, in a collaboration between universities and industrial partners, we have constructed a complex ion-based quantum processor with the goal of realizing a logical quantum bit. I will briefly report on the performance of our first-generation integrated system, including fidelities of single-qubit and two-qubit gates, crosstalk, operation with long ion chains, and syndrome readout.

One of the factors limiting performance of a large trapped ion quantum processor is excess electric-field noise that causes ion heating. I will report results from electric-field noise studies performed at high temperatures, in which we observe a nontrivial temperature dependence with the noise amplitude at 1 MHz frequency saturating around 500 K. This behavior can be explained by considering noise from a distribution of thermally activated two-level fluctuators with activation energies between 0.35 and 0.65 eV. Processes in this energy range may be relevant to understanding electric-field noise in ion traps; for example, defect motion in the solid state and surface adsorbate binding energies. The study of these processes may aid in identification of the origin of excess electric-field noise in ion traps.

*This work is supported by the ARO with funding from the IARPA LogiQ program, the NSF Practical Fully-Connected Quantum Computer program, the DOE program on Quantum Computing in Chemical and Material Sciences, the AFOSR MURI on Quantum Measurement and Verification, and the AFOSR MURI on Interactive Quantum Computation and Communication Protocols.

**Sara Mouradian, University of California, Berkeley (Haeffner group)**

Increasing connectivity in complex quantum systems

Engineered quantum systems are often limited to a handful of nodes with limited - and often immutable - connectivity. Here I will introduce two quantum systems that promise to overcome these limitations - the negatively charged nitrogen vacancy center in diamond and trapped atomic ions. I will compare their unique benefits and drawbacks as building blocks for complex quantum systems and discuss the engineering challenges that must be overcome to realize their full potential.

**Christian Kraglund Andersen, ETH Zürich (Wallraff group)**

Designing and operating superconducting circuits for quantum error correction

In recent years, quantum computing has seen a surge of progress both theoretically and experimentally. However, the long-term success of quantum computers relies on the ability to perform fault-tolerant quantum computations using quantum error correction. In this approach, errors are detected through the repeated measurement of multi-qubit parity operators and corrected using feedback operations conditioned on the measurement outcomes. In this talk, I will discuss recent progress towards demonstrating the feasibility of quantum error correction with superconducting qubits. I will show an experiment using of an ancillary qubit to repeatedly measure the ZZ and XX parity operators of two data qubits and to thereby project their joint state into the respective parity subspaces. By applying feedback operations conditioned on the outcomes of individual parity measurements, we demonstrate the real-time stabilization of a Bell state with a fidelity of F≈74% in up to 12 cycles of the feedback loop [1]. The ability to stabilize parity over multiple feedback rounds with no reduction in fidelity provides strong evidence for the feasibility of executing stabilizer codes on timescales much longer than the intrinsic coherence times of the constituent qubits. I finally discuss our current efforts in scaling up to larger error-correction schemes.

Reference:

[1] C.K. Andersen, et al., arXiv:1902.06946 (2019)

**Chiao-Hsuan Wang, University of Chicago (Jiang group)**

Autonomous quantum error correction by Hamiltonian and dissipation engineering

Autonomous quantum error correction (AutoQEC) utilizes an engineered coupling between a quantum system and a dissipative ancilla to protect encoded logical quantum information against physical errors. It has been recently shown that if a code space satisfies the Knill-Laflamme condition for the Markovian error generators (plus identity operator), there exists a set of engineered dissipative jump operators such that the logical error probability vanishes in the limit of infinitely strong engineered dissipation.

Here we apply the general theory of AutoQEC to bosonic error-correcting codes, and propose an explicit Hamiltonian and dissipation engineering method to protect the encoded information against photon loss errors. Specifically, we demonstrate a scheme for autonomously stabilizing cavity cat states in the presence of photon loss, which admits potential experimental implementations in circuit quantum electrodynamics systems.

**Maritn Sandberg, IBM **

Plenary talk: Superconducting quantum circuits as a path for quantum computing

Quantum computing has received a lot of attention because of its potential of solving computational problems that are considered unsolvable on classical computers. The field has for a long time been driven by academic research but in recent years the interest from industry has gained a lot of momentum. One advantage of a large-scale industry research effort is that several very diverse problems can be addressed. In order for quantum computing to become reality a multitude of problems needs to be solved; hardware, software, electronics and theory all needs to come together as one system. Having expertise in all these areas within a single organization can be a great strength. IBM has pioneered the efforts of building quantum computing systems fully accessible to the public through the could. IBM is currently operating 10 quantum processors both for public and commercial use. In this talk I will give an overview of superconducting quantum circuits, with focus on the challenges we are facing as we scale up to larger circuits. In addition, I will discuss aspects of being an industry-based researcher in this fast-moving field.

**Zlatko Minev, IBM and Yale University (Devoret group)**

To catch and reverse a quantum jump mid-flight

In quantum physics, measurements can fundamentally yield discrete and random results. Emblematic of this feature is Bohr’s 1913 proposal of quantum jumps between two discrete energy levels of an atom. Experimentally, quantum jumps were first observed in an atomic ion driven by a weak deterministic force while under strong continuous energy measurement. The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Despite the non-deterministic character of quantum physics, is it possible to know if a quantum jump is about to occur? Here we answer this question affirmatively: we experimentally demonstrate that the jump from the ground state to an excited state of a superconducting artificial three-level atom can be tracked as it follows a predictable ‘flight’, by monitoring the population of an auxiliary energy level coupled to the ground state. The experimental results demonstrate that the evolution of each completed jump is continuous, coherent and deterministic. We exploit these features, using real-time monitoring and feedback, to catch and reverse quantum jumps mid-flight—thus deterministically preventing their completion. Our findings, which agree with theoretical predictions essentially without adjustable parameters, support the modern quantum trajectory theory and should provide new ground for the exploration of real-time intervention techniques in the control of quantum systems, such as the early detection of error syndromes in quantum error correction [1].

Reference:

[1] Nature volume 570, pages 200–204 (2019)

**Alexandre Cooper-Roy, University of Waterloo **

Plenary talk: An atomic array optical clock with single-atom readout

Reconfigurable arrays of neutral atoms excited to Rydberg states provide a versatile experimental platform to study many-body quantum dynamics in various geometries with tunable interactions and microscopic control. I will first describe our ongoing effort at the University of Waterloo to deliver such quantum simulators to early adopters. I will then describe our recent work from Caltech on operating atomic array optical clocks using bosonic strontium atoms in tweezer arrays [1-3].

References:

[1] A. Cooper *et al.*, PRX 8, 041055 (2018)

[2] J. P. Covey *et al*., PRL 122, 173201 (2019)

[3] I. S. Madjarov *et al*., arXiv:1908.05619 (2019)

**Ahmed Omran, Harvard University (Lukin group)**

Controlling entanglement in Rydberg atom arrays

Programmable arrays of neutral atoms provide an exciting avenue for quantum sim- ulations and quantum information processing. We employ a 1D array of neutral atoms coupled to Rydberg states to simulate a transverse-field Ising model with long-range in- teractions. This system can undergo quantum phase transitions breaking different spatial symmetries, which we can study in detail.

I will describe a method we developed to rapidly prepare Greenberger-Horne-Zeilinger (GHZ) states with up to 20 atoms using site resolved engineering of the many-body spectrum and optimal control of the quantum many-body system. Furthermore, our local addressing enables the demonstration of entanglement distribution to distant sites in the array and high-fidelity quantum logic gates. The ability to reliably produce and manipulate entanglement in neutral atom systems opens up a new route towards scalable quantum processors.

**Aziza Suleymanzade, University of Chicago (Simon & Schuster groups)**

The circuit- and cavity-QED systems are essential tools for exploring quantum phenomena both in the optical and microwave regimes, while millimeter-waves remain relatively unexplored. As a quantum platform, mm-wave frequencies offer an abundance of 100GHz resonances in commonly used emitters, single photon resolution at temperatures higher that 1K and unusual length scale for making devices both in the far and near field regimes. In my talk, I will, first, introduce mm-wave frequencies as a potential band for quantum computation at high cryogenic temperatures. Then, I will outline our progress towards a hybrid experimental system for creating strong interactions between single optical and mm-wave photons with Rydberg atoms as the interface. I will present our recent results, including the realization of the crossed high-Q mm-wave and optical cavity at 4K and the observation of the Vacuum Rabi splitting. Finally, I will briefly mention our efforts in mm-wave devices beyond Rydberg-cavity QED systems, such as 2D nonlinear resonators, 100 GHz parametric amplifier and other high-Q devices in this frequency band.

**Boris Braverman, University of Ottawa (Boyd group)**

Near-unitary spin squeezing with Ytterbium

State of the art atomic sensors operate near the standard quantum limit (SQL) of projection noise, where the precision scales as the square root of the particle number. Overcoming this limit by using atom-atom entanglement such as spin squeezing is a major goal in quantum metrology.

Spin squeezing can be realized with the techniques of cavity quantum electrodynamics (cQED) by coupling an atomic ensemble to a high-finesse optical resonator. The resulting collective atom-light interaction allows for both measurement and cavity feedback squeezing. These methods for producing spin squeezing are typically non-unitary and generate more anti-squeezing than the minimum prescribed by the uncertainty principle, due to a residual entanglement between the atomic ensemble and probing photons. We find that non-unitarity significantly lowers the potential metrological gain from squeezing in atomic clocks and other quantum sensors.

We couple an ensemble of approximately 1000 Yb-171 atoms to a high- finesse asymmetric micromirror cavity with single-atom cooperativity of 1.8. A laser pulse induces an effective one-axis twisting Hamiltonian for the atoms, producing the desired squeezed spin state (SSS). We detune the probing light from atomic and cavity resonance by several linewidths to limit the undesirable entanglement between atoms and light.

We characterize the produced SSSs by state tomography, measuring the zquadrature variance after a rotation by a variable angle. For moderate normal- ized atom-atom interaction strength, we observe states with a nearly equal level of noise reduction and enhancement, confirming the production of a near-unitary spin squeezed state. The observed spin noise suppression and metrological gain are limited by the state readout to 9.4(4) dB and 6.5(4) dB, respectively, while the generated states offer a spin noise suppression of 15.9(6) dB and a metrological gain of 12.9(6) dB over the standard quantum limit (SQL), limited by the curvature of the Bloch sphere. When requiring the squeezing process to be within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2).

This experimental platform will allow for the creation of quantum states with metrologically useful entanglement on the clock transition of Yb-171.