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Monday, October 15, 2018

Lazaridis QNC 0101

9:00 am  Opening remarks
9:10 am

Mukund Vengalattore, Cornell University

Emergent phases and Criticality in open quantum systems : Universality beyond the Markovian regime

9:55 am

Nils J. Engelsen, École Polytechnique (Tobias Kippenberg group)

Ultralow mechanical dissipation for quantum optomechanics

10:40 am Coffee break
11:00 am

Vera Schäfer, Oxford University (David Lucas group)

Plenary talk: Fast entangling gates with trapped ions

11:45 am

Michael Gullans, Princeton University (David Huse group)

Entanglement structure of current driven diffusive fermion systems

12:30 pm Lunch
1:15 pm

Shruti Puri, Yale University (Steven Girvin group)

Quantum error correction when the noise is strongly biased

2:00 pm

Serge Rosenblum, Yale University (Robert Schoelkopf group)

Fault-tolerant detection of quantum errors

2:45 pm Coffee break
3:05 pm

Sydney Schreppler, University California Berkeley

(Irfan Siddiqi group)

Qubit dress codes: Quantum measurement and entanglement with driven transmons

3:50 pm

Alexandre Cooper-Roy, California Institute of Technology

(Manuel Endres group)

Single alkaline-earth atoms in reconfigurable arrays of optical tweezers with Rydberg interactions

4:45 pm

Reception with Institute for Quantum Computing faculty

Lazaridis QNC 2101

6:00 pm QNC lab tours

Tuesday, October 16, 2018

Lazaridis QNC 0101

9:00 am

Raisa Trubko, Harvard-Smithsonian Centre for Astrophysics

(Ron Walsworth & Roger Fu group)

Precision Tune-Out Wavelength Measurements with Atom Interferometry

9:45 am

Qiyu Liang, University of Maryland (Ian Spielman group)

Observation of a three-photon bound state

10:30 am

Coffee break

10:50 am

Susanne Yelin, University of Connecticut and Harvard University

Plenary talk: Quantum optics with two-dimensional atomic arrays

11:50 am

Natalia Bruno, The Institute of Photonic Sciences

(Morgan Mitchell group)

Interfacing a single trapped atom to a pair of indistinguishable photons

12:35 pm

Lunch and group picture

1:20 pm Career panel discussion
3:00 pm

Jelena Vučković, Stanford University

Plenary talk: Connecting quantum systems through optimized photonics

4:00 pm Coffee break
4:30 pm

Silvia Arroyo Camejo, Siemens Medical Technologies

(Stefan Hell group)

Robust, high-fidelity quantum gates for fault-tolerant, large-scale quantum computers

5:15 pm

Yelena Guryanova, Austrian Academy of Sciences

(Marcus Huber group)

Ideal Projective Measurements Have Infinite Resource Costs

6:30 pm Banquet at the University Club

Wednesday, October 17, 2018

RAC 1 2009

9:00 am

Kristan Corwin, Kansas State University

Plenary talk: Developments in optical frequency comb spectroscopy

10:00 am

Kevin Fischer, Stanford University (Jelena Vučković group)

Generation of pulsed nonclassical light

10:45 am Coffee break
11:05 am

Helena Knowles, Harvard University (Mikhail Lukin group)

Probing and controlling dark spin ensembles using nitrogen- vacancy centers in diamond

11:50 am

Ashok Ajoy, University of California, Berkeley

(Alexander Pines group)

Quantum assisted sensing across length scales

12:35 pm Lunch
1:30 pm

Shuo Sun, Stanford University (Jelena Vučković group)

Quantum nanophotonics: engineering atom-photon interactions on a chip

2:15 pm

Ruffin Evans, Harvard University (Mikhail Lukin group)

Photon-mediated interactions between quantum emitters in a diamond nanocavity

3:00 pm Coffee break
3:15 pm

Luis A. Jauregui, Harvard University (Philip Kim group)

Engineering novel optoelectronic devices based on interlayer excitons in van der Waals heterostructures

4:00 pm

Christopher Gutiérrez, University of British Columbia

(Andrea Damascelli group)

Quantum donuts & wedding cakes: Topology- and interaction-driven effects in graphene quantum dots

4:45 pm RAC 2 lab tours
7:00 pm BBQ @ RAC 2

Thursday, October 18, 2018

Lazaridis QNC 0101

9:00 am

Virginia O. Lorenz, University of Illinois at Urbana-Champaign

Plenary talk: Photonic quantum states for quantum applications

10:00 am

Rivka Bekenstein, Harvard University (Mikhail Lukin group)

From gravity with optical systems to quantum metasurfaces

10:45 am Coffee break
11:05 am

Jeongwon Lee, Massachusetts Institute of Technology

(Wolfgang Ketterle group)

Ultracold Atoms and Molecules for Quantum Simulation: From Spin-orbit Coupling to Supersolidity

11:50 am

Christine Muschik, Institute for Quantum Computing

Plenary talk: How to simulate models from high energy physics in a trapped-ion experiment

12:50 pm Closing remarks
1:00 pm Lunch

Abstracts

Mukund Vengalattore, Cornell University

Emergent phases and Criticality in open quantum systems : Universality beyond the Markovian regime

All qubit and quantum sensor platforms are inherently ‘open quantum systems’, i.e. they interact constantly with the environment. While such environmental influences predominantly lead to the destruction of quantum coherence, there is growing realization that artificially engineered dissipation or ‘reservoir engineering’ techniques can, counter-intuitively, lead to novel and robust forms of quantum behavior in a wide range of quantum systems. I will discuss our experimental implementation of ‘reservoir engineered’ open quantum systems in a diverse array of physical platforms including ultracold atoms, optomechanical devices and hybrid quantum systems. We find that the interplay between intrinsic quantum dynamics and engineered dissipation can lead to emergent dynamical phases with robust, topologically protected forms of quantum coherence and entanglement. I will discuss applications of these phases to quantum-enhanced metrology and sensor capabilities. Lastly, I will also discuss the universal scaling properties and critical behavior of these emergent phases. Our findings of universal critical behavior of reservoir-engineered quantum phases can potentially serve as a touchstone for the extension of these concepts to other physical systems including trapped ions, solid-state defect centers and superconducting qubits.

Nils J. Engelsen, École Polytechnique

Ultralow mechanical dissipation for quantum optomechanics

Reduced mechanical dissipation is of great importance for both precision sensing and fundamental science, such as quantum optomechanics. I will describe two techniques for reducing mechanical dissipation, here implemented in thin-film Si3N4 nanobeams. The first technique, ‘soft clamping’, utilizes a phononic crystal to create an incomplete mechanical bandgap with a localized, flexural mechanical mode. By combining soft clamping with elastic strain engineering, where the strain is increased in the region of mode localization, we obtained quality factors as high as 800 million for a 1.3 MHz mechanical mode. I will then discuss how these two techniques can be applied to crystalline materials to reach higher quality factors. Finally, I will outline our efforts to integrate these mechanical oscillators in new systems for quantum optomechanics.

Vera Schäfer, Oxford University

Plenary talk: Fast entangling gates with trapped ions

Trapped ion qubits are one of the most promising candidates for scalable quantum computing. Entangling gates with trapped ions achieve higher fidelities than in any other system, but are typically performed in an adiabatic regime, where the motional frequencies of the ions in the trap limit the gate speed. Many schemes have been proposed to overcome these limitations, but have only now been successfully implemented [1, 2]. Following [3] we use amplitude-shaped cw-pulses to perform entangling gates significantly faster than the speed limit for conventional gate mechanisms. At these gate speeds, the motional modes are not spectrally isolated, leading to entanglement with both motional modes sensitively depending on the optical phase of the control fields. We demonstrate gates with fidelity F = 99.8% in 1.6 µs [2] - over an order of magnitude faster than previous trapped ion gates of similar fidelity. We also perform entanglement generation for gate times as short as 480 ns - this is below a single motional period of the ions.

Michael Gullans, Princeton University

Entanglement structure of current driven diffusive fermion systems

Applying a chemical potential bias to a conductor drives the system out of equilibrium into a current carrying non-equilibrium state.  This current flow is associated with entropy production in the leads, but it remains poorly understood under what conditions the system is driven to local equilibrium by this process.  We investigate this problem using two toy models for coherent quantum transport of diffusive fermions:  Anderson models in the conducting phase and a class of random quantum circuits acting on a chain of qubits, which exactly maps to an interacting fermion problem. Under certain conditions, we find that the long-time states in both models exhibit volume-law mutual information and entanglement, in striking violation of local equilibrium.  Extending this analysis to Anderson metal-insulator transitions, we find that the volume-law entanglement scaling persists at the critical point up to mobility edge effects.  This work points towards a broad class of examples of physical systems where volume-law entanglement can be sustained, and potentially harnessed, despite strong coupling of the system to its surrounding environment.

Shruti Puri, Yale University

Quantum error correction when the noise is strongly biased

In this talk I will present a bosonic cat-qubit stabilized against phase-flips in a parametrically driven nonlinear cavity. Such a cat-qubit exhibits a strongly biased noise channel and has far reaching implications for quantum error correction (QEC). Firstly, I will show that it can be used as an ancilla for hardware-efficient, fault-tolerant syndrome extraction in a variety of error correcting codes such as the qubit based toric codes, bosonic cat and gkp codes. Secondly, I will describe a platform for large-scale fault-tolerant quantum computation based on these stabilized cat-qubits. The biggest challenge for QEC with biased noise is to be able to maintain the bias while performing elementary operations. I will introduce a set of bias-preserving gates that can be performed with the stabilized cat-qubit. Our results open a path for designing error correction schemes with ultrahigh thresholds and reduced overhead requirements.

Serge Rosenblum, Yale University

Fault-tolerant detection of quantum errors

Future quantum processors will require repeated detection and correction of errors in order to operate in a noisy environment. However, the process of error correction is itself faulty, as errors in the ancilla detection system can propagate onto the logical qubits and corrupt the encoded information. Fault tolerance is therefore essential for scaling up error corrected quantum computation.

We realize a fault-tolerant error detection scheme that suppresses spreading of ancilla errors by a factor of five, while maintaining the assignment fidelity [1]. The same method is used to prevent propagation of thermal ancilla excitations, increasing the logical qubit dephasing time by an order of magnitude. Our approach is hardware efficient, as it uses a single multilevel transmon ancilla and a cavity-encoded logical qubit, whose interaction is engineered in situ using an off-resonant sideband drive. These results demonstrate that fault tolerance can be implemented hardware-efficiently by exploiting physically relevant error models.

Sydney Schreppler, University California Berkeley

Qubit dress codes: Quantum measurement and entanglement with
driven transmons

Quantum simulators of analog and digital varieties rely on the ability to entangle and measure constituent particles with high fidelity. I will describe a method of arranging energy levels of superconducting transmon qubits using microwave dressing that, when combined with a stroboscopic dispersive tone, induces a response analogous both to back-action evading measurements in cavity optomechanics and to stimulated Raman transitions in trapped ions. With this stroboscopic scheme, we have experimentally demonstrated improved qubit measurement using squeezed vacuum. We now expand the interaction to drive multi-qubit entangling gates via shared photonic modes. This new functionality encourages development of hybrid analog-digital approaches to quantum simulations with superconducting qubits.

Alexandre Cooper-Roy, California Institute of Technology

Single alkaline-earth atoms in reconfigurable arrays of optical tweezers with Rydberg interactions

Single neutral atoms in reconfigurable arrays of optical tweezers offer a promising plateform for assembling many-body interacting quantum systems and exploring their applications to quantum computation and quantum simulation. In particular, alkaline-earth atoms offer narrow optical transitions for achieving efficient cooling, ultra-narrow optical clock transitions for implementing high-fidelity single-qubit operations, and strong excitation to Rydberg states for engineering interatomic interactions. In this talk, I will present our recent experimental results demonstrating the imaging and cooling of single strontium atoms in optical tweezers near a magic wavelength. First, I will describe a novel cooling mechanism to compensate for recoil heating during fluorescence imaging. Then, I will show how tuning the polarization of the optical tweezer enables reaching a magic trapping condition so as to cool down strontium atoms near their motional ground state using resolved sideband cooling. Finally, I will discuss approaches to scaling up our system to larger dimensions and engineering interactions through direct excitation to Rydberg states. This work paves the way for assembling alkaline-earth atoms in large defect-free arrays of optical tweezers with arbitrary geometry and tunable interactions to explore many-body spin dynamics and solve complex optimization problems. 

Raisa Trubko, Harvard-Smithsonian Centre for Astrophysics

Precision Tune-Out Wavelength Measurements with Atom Interferometry

Precision measurements of atomic properties are important because they serve as a benchmark test of atomic structure calculations of line strengths, oscillator strengths, and dipole matrix elements. In this talk, I will describe how I used a three nanograting Mach-Zehnder atom beam interferometer to make precision measurements of atomic properties, such as polarizabilities and tune-out wavelengths (where the polarizability is zero). I will present my measurement of the longest tune-out wavelength in potassium, 768.9701(4) nm. This result is 7.5 times more precise than state-of-the-art calculations. I will also explain how tune-out wavelength measurements can be remarkably sensitive to rotation rates and will demonstrate a new type of atom interferometer gyroscope that uses tune-out wavelengths.

Lastly, I will describe my current research, where I use nitrogen-vacancy centers in diamond to measure magnetic fields with high spatial resolution. This work helps answer open questions on the formation of the solar system and Earth.

Qiyu Liang, University of Maryland

Observation of a three-photon bound state

Bound states of massive particles, be it in the form of nucleons, atoms or molecules, are ubiquitous, and constitute the bulk of the visible world around us. In contrast, photonphoton interactions are weak and need to be specifically engineered in the form of nonlinear optical media. Here we report the observation of a three-photon bound state inside a quantum nonlinear optical medium. The strong photon-photon interaction is achieved by coupling the light to highly excited, strongly interacting Rydberg states in a cold atomic gas. The photonic trimer is observed via bunching and a strongly nonlinear phase in the three-photon correlation function of the emerging light. The observations are quantitatively described by an effective field theory of Rydberg-induced photonphoton interactions, and agree with direct numerical simulations. This work paves the way towards the realization, understanding, and control of strongly interacting quantum gases of light.

Susanne Yelin, University of Connecticut and Harvard University

Plenary talk: Quantum optics with twodimensional atomic arrays

We consider quantum optical phenomena in two-dimensional (2D) dipolar arrays with sub-wavelength spacing. We show that cooperative resonances of the surface modes in such arrays allow for implementation of a nearly perfect atomically thin mirror, shaping of the emission patterns from individual quantum emitters, and realization of topological quantum optical systems. Experimental implementation using ultracold arrays of trapped atoms and excitons in atomically thin semiconductor materials will be discussed. Potential applications ranging from atomically thin metasurfaces to quantum optomechanics and quantum photon nonlinear optics will be described.

Natalia Bruno, The Institute of Photonic Sciences

Interfacing a single trapped atom to a pair of indistinguishable photons

We describe a novel system to interact atom-resonant single photons and photon pairs with individual trapped atoms at the focus of four high-NA lenses. Merging an atom-resonant cavity-enhanced SPDC photon source with a single trapped atom and having optical access from two directions allows us to observe light matter interaction and study phenomena such as stimulated emission in the single particle regime, or multi-photon quantum interference using an atom as a beam-splitter.

Jelena Vučković, Stanford University

Plenary talk: Connecting quantum systems through optimized photonics

Color centers in wide bandgap materials, such as silicon vacancy (SiV) in diamond, represent a promising platform for implementation of quantum technologies: they exhibit a small spectral inhomogeneity and a minimal sensitivity to environment, which facilitates their incorporation in scalable devices. Excellent SiV-photon interfaces have been demonstrated (by embedding them in cavities) with large cooperativities and Purcell enhancements. We have also demonstrated cavity enhanced Raman scattering from a single SiV for detuning of up to 100GHz - well beyond 30GHz of spectral inhomogeneity observed for SiVs embedded in structures, which enables experiments incorporating multiple SiVs. However, in addition to high quality qubits interfaced to photons, successful implementation of quantum technologies also requires photonic circuits that are scalable, robust to errors, and exhibit minimal losses. Our recent work on inverse design in photonics offers a powerful tool to design and implement photonic circuits with superior properties, including robustness to errors in fabrication and temperature, compact footprints, novel functionalities, and high efficiencies. We have applied this approach to diamond quantum hardware, leading to greater than an order of magnitude of improvement in efficiencies and a dramatic reduction in experimental times, thereby opening opportunities for new experiments, including implementation of solid state quantum simulators.

Silvia Arroyo Camejo, Siemens Medical Technologies

Robust, high-fidelity quantum gates for fault-tolerant, large-scale quantum computers

Currently we reside in an exciting era, in which large-scale circuit-based quantum computers do not exist yet, but their realization appears to become feasible. This era of ‘Noisy Intermediate-Scale Quantum Computers’(NISQ) [1] offers circuit-based computing platforms with O(10) physical qubits and quantum annealers acting on O(103) physical qubits. Despite these impressive achievements in scaling-up the number or qubits, a profound challenge for building viable quantum robustness of the quantum gates are significantly improved, can quantum error correction codes be efficaciously deployed, and thus universal large-scale quantum computation will become a reality. In this talk I will report of several strategies to implement intrinsically robust, high-fidelity quantum gates based on geometric phases[2]. In our recent experimental work we have explored both nonadiabatic geometric phases (Abelian)[2] and non-adiabatic holonomies (non-Abelian)[3,4]to realize intrinsically robust quantum gates. We experimentally implemented these quantum control strategies [5,6] on an NV center electron spin in diamond and performed a benchmark analysis. Our results suggest that a universal set of quantum gates should be composed hybridly, picking the most suitable quantum control strategy for each logic gate, while considering the experimentally dominant noise parameters.

Yelena Guryanova, Austrian Academy of Sciences

Ideal Projective Measurements Have Infinite Resource Costs

We show that it is impossible to perform ideal projective measurements on quantum systems using finite resources. We identify three fundamental features of an ideal projective measurement and show that when limited by finite resources only one of these features can be salvaged. Using an explicit model of an N-particle detector perfectly reproducing the statistics of the system, we provide tight analytic expressions for the energy cost of performing a measurement. This cost may be broken down into two parts. First, the cost of preparing the pointer in a suitable state, and second, the cost of a global interaction between the system and pointer in order to correlate them. Our results show that, even under the assumption that the interaction can be controlled perfectly, achieving perfect correlation is infinitely expensive. We provide protocols for achieving optimal correlation given finite resources.

Kristan Corwin, Kansas State University

Plenary talk: Developments in optical frequency comb spectroscopy

Optical frequency combs have transformed the science of precision measurement of optical frequencies. More recently, entanglement between modes of down‐converted frequency combs has been observed, making them an interesting source to explore for quantum information. In addition, dual‐comb spectroscopy has opened up many applications, including detection of gases over large integrated pathways in a field‐deployable way. Expansion of these combs into the XUV and mid‐IR further broadens the applications of frequency comb spectroscopy. In this talk, I will describe recent advances in frequency comb generation across the electromagnetic spectrum, and elaborate on a project to use frequency combs for the detection of agriculturally relevant gases.
 

Kevin Fischer, Stanford University

Generation of pulsed nonclassical light

One of the most efficient ways to mediate quantum information is with the photonic field, which requires the deterministic production of target states of nonclassical light, such as single isolated photons. In this talk, I will overview our fundamental research on the generation of few-photon photon pulses. A promising materials platform for this task is the InAs/GaAs quantum dot, which can be mostly understood as a few-level quantum system. Its role in generating nonclassical light can be thought of as a highly nonlinear filter that extracts just a few photons from an incident laser pulse. I will present experimental works showing how we have achieved nearly ideal single-photon generation, and have begun to explore two-photon generation. The experimental work is paired with a theory of how quantum systems generate pulses of light, which provides a new foundation for understanding theoretical quantum optics.

Helena Knowles, Harvard University

Probing and controlling dark spin ensembles using nitrogen- vacancy centers in diamond

A single isolated spin in a solid can act as a unit of a quantum network or as an individual magnetic or electric field sensor. Such a unit can be expanded by using coherently interacting spin clusters, which provide a performance enhancement for quantum technologies.

In this talk, I will show how we investigate hybrid spin systems composed of the NitrogenVacancy centre (NV) in diamond coupled to dark spins, i.e. spins that are not directly optically accessible. We achieve sub-nm localization of a proximal nitrogen (N) impurity cluster and perform environment-assisted sensing: An entangled state of the NV and N spins is used to detect an external magnetic field and we observe a double-frequency component in the interferometer signal, corresponding to the contribution of at least two electronic spins, in contrast to the NV spin only.

 I will also introduce the NV centre as a probe for studying nuclear spin dynamics in two dimensional materials. In this experiment we locally initialise and control a nuclear spin ensemble inside hexagonal boron nitride, with the goal of developing a room temperature platform for studying many-body dynamics.

Ashok Ajoy, University of California, Berkeley

Quantum assisted sensing across length scales

The development of point-like quantum sensors based on wide bandgap materials, for instance Nitrogen Vacancy (NV) centers in diamond, has thrown up exciting new possibilities for the sensing of materials, molecules and biological systems through optical means. In particular the development of magnetic resonance probes based on the NV center has shown tremendous promise for the sensing of nano- and meso-scale volumes at high spatial and frequency resolution. In this talk I will outline our efforts in this direction, and particularly focus on an alternate use of the NV sensor as a means to create highly nonequilibrium spin populations in nuclear spin systems in order to “hyperpolarize” them, boosting their magnetic resonance signatures by several orders of magnitude. This allows quantum sensors to greatly boost the sensing capabilities of conventional macro-scale MRI and NMR, potentially enabling compelling possibilities such as the development of miniature spectrometers for high-throughput chemical analysis and metabolite tracking.

Shuo Sun, Stanford University

Quantum nanophotonics: engineering atom-photon interactions on a chip

The ability to engineer controllable atom-photon interactions is critical for quantum information processing and quantum networking. In this talk, I will introduce how we utilize a nanophotonic platform to engineer strong atom-photon interactions on a semiconductor chip. I will first discuss an experimental demonstration of a spin-photon quantum transistor, where a single solid-state spin trapped inside a quantum dot could switch a single photon, and vice versa, a single photon could flip the spin. I will discuss how the spin-photon quantum transistor can realize high-fidelity all-optical spin readout and a single-photon transistor, where a single gate photon can switch many signal photons on-a-chip. I will next discuss the promise of realizing photon-mediated many-body interactions in an alternative solid-state platform based on siliconvacancy (SiV) color centers in diamond. I will introduce our efforts in creating strong light-matter interactions through photonic crystal cavities fabricated in diamond, and the use of cavitystimulated Raman emission to overcome the remaining frequency inhomogeneity of SiVs. Finally, I will outline the exciting prospects of applying inverse designed nanophotonic structures into quantum optics, and their applications in engineering many-body interactions with tunable Hamiltonians.

Ruffin Evans, Harvard University

Photon-mediated interactions between quantum emitters in a diamond nanocavity

Photon-mediated interaction between quantum systems are essential for realizing quantum networks and scalable quantum information processing. We demonstrate such interactions between pairs of silicon-vacancy (SiV) color centers coupled to a diamond nanophotonic cavity. When the optical transitions of the two color centers are tuned into resonance, the coupling to the common cavity mode results in a coherent interaction between them, leading to spectrally-resolved super radiant and sub radiant states. We use the electronic spin degrees of freedom of the SiV centers to control these optically-mediated interactions. Such controlled interactions will be crucial in developing cavity-mediated quantum gates between spin qubits and for realizing scalable quantum network nodes.

Luis A. Jauregui, Harvard University

Engineering novel optoelectronic devices based on interlayer excitons in van der Waals heterostructures

Van der Waals (vdW) heterostructures built of 2-dimensional (2D) materials, such as single layer transition metal dichalcogenides (TMDs) and boron nitride (h-BN), have generated wide interest to investigate novel optoelectronic devices. The large excitonic binding energy of TMDs and their intrinsic 2D nature allow for interesting ways to explore novel quantum optical effects in TMDs. I will discuss our recent results of vdWs heterostructures formed by stacking together two different TMDs (a type-II heterostructure) encapsulated with h-BN with electrical contacts and dual gate configuration (as shown in Fig. 1a). Using an optical excitation, we generate excitons with the electron and the hole each residing in the two different TMDs (interlayer excitons, IE). Thus, IEs have a dipole moment oriented out-of-plane and are repulsive in nature, because of the Coulomb interaction. With increasing excitation power, we create a large density of IEs (5x1011 cm-2 ) and observe long transport distances ~ 20µm (as shown in Fig. 1b - d) even at elevated temperatures (T = 60K). Because the IEs move from areas of larger density and temperature (the excitation spot), to regions outside the hot generation spot, they create a cold gas of bosons. Using multiple gates we can create electrostatic traps with densities in the order of 1.5-3x1012 cm-2 . A large density of IEs is important for novel optoelectronic devices such as IE condensates and lasers.

Christopher Gutiérrez, University of British Columbia

Quantum donuts & wedding cakes: Topology- and interaction-driven effects in graphene quantum dots

Graphene is a quasi two-dimensional material with low-energy excitations that can be described by the relativistic Dirac equation for massless chiral fermions. Recently, the ability to generate nanoscale substrate gate potentials has opened the door for creating confined quantum dot (QD) states in a contiguous sheet of graphene. Unlike other QD systems, graphene’s exposed electronic surface is uniquely amenable to scanning probe measurements that reveal the spatial structure of the resonant QD states. In this talk I will present scanning tunneling microscopy/spectroscopy (STM/S) measurements that explore the interplay between spatial and magnetic confinement in graphene QDs. I will show how the application of a weak magnetic field (B ~ 0.1 mT) can act as a topological Berry phase on/off “switch” resulting in the sudden onset of large energy splittings in the graphene QD spectrum. At higher fields (B > 1T), we directly visualize the intricate evolution of the QD resonant states into highly degenerate Landau levels where electron interactions lead to the subsequent formation of a ‘wedding cake’- like structure of compressible-incompressible strips.

Virginia O. Lorenz, University of Illinois at Urbana-Champaign

Plenary talk: Photonic quantum states for quantum applications

Quantum computing and quantum communication applications often require the carriers of information, or qubits, to have specific properties. Photonic quantum states are good carriers of information because they are robust to environmental fluctuations, but generating photons with just the right properties is still a challenge. I will present our work on generating, engineering and characterizing photonic quantum states for quantum applications.

Rivka Bekenstein, Harvard University

From gravity with optical systems to quantum metasurfaces

A century passed since Einstein published the theory of General Relativity (GR), and some predictions of GR still elude observation. Hence, analogous systems, such as optical systems, have been suggested as emulation platforms. Most importantly, we still lack a unifying theory of gravity and quantum mechanics. Can we learn anything toward this theory from simulating systems?

I will first discuss my simulation of the Newton-Schrödinger model in a nonlinear optical experiment. GR is inherently nonlinear: for example, masses dynamics is affected by the curved space they themselves induce. However, thus far all GR optical emulation demonstrated linear dynamics, where fix curved background determines the evolution of the electromagnetic waves. In my experiment, I demonstrated analogous gravitational effects with optical wavepackets under a long-range thermal nonlinearity. This optical system is mathematically equivalent to the Newton–Schrödinger model, which has been studied strictly theoretically. It describes a mass density evolving according to the Schrödinger equation in the presence of a gravitational potential created by the mass density itself, and is mostly important due to the lack of a unified theory of quantum gravity. These wavepackets interact by the curved space they themselves induce, exhibiting complex nonlinear dynamics arising from the interplay between diffraction and the emulated gravity. I have observed emulated gravitational lensing, tidal forces and gravitational redshift in this system, including modification of these phenomena that rise due to the nonlinear nature of gravity which exists in the Newton–Schrödinger model.

I will then give an overview of my current research at Harvard, where I am emulating curved space for light using a quantum optical system, while pursuing understanding of the relation between curved space and quantum science.  I will introduce our new concept of quantum metasurfaces using strongly interacting atoms and its potential applications to quantum information.

Jeongwon Lee, Massachusetts Institute of Technology

Ultracold Atoms and Molecules for Quantum Simulation: From Spin-orbit Coupling to Supersolidity

Ultracold atoms trapped in laser light have emerged as a platform to emulate various condensed matter phenomena due to its defect-free nature and high degree of controllability. In particular, there has been great interest towards spin-orbit coupled ultracold atoms because they can be used to illustrate fundamental aspects of topology in physics, and to explore possible applications in quantum information and spintronics. In this talk, I will present our new scheme of generating a spin-orbit coupled Bose-Einstein condensate (BEC) in an optical superlattice, and how it enabled us to directly observe a stripe phase with supersolid properties. Our work establishes a system with unique continuous symmetry breaking properties. Further investigations on collective excitations and the role of disorder in our system will push the frontiers of quantum material science. Moving forward, I will discuss the potential of utilizing ultracold molecules to create a new system with long-range dipolar interactions, which opens the door for simulating quantum many body physics.

Christine Muschik, Institute for Quantum Computing

Plenary talk: How to simulate models from high energy physics in a trapped-ion experiment

Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. However, computing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods. In the spirit of Feynman's vision of a quantum simulator, this has recently stimulated theoretical effort to devise schemes for simulating such theories on engineered quantum-mechanical devices, with the difficulty that gauge invariance and the associated local conservation laws (Gauss laws) need to be implemented. We propose and experimentally demonstrate of a digital quantum simulation of a lattice gauge theory, by realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a few-qubit trapped-ion quantum computer. Our work represents a first step towards quantum simulating high-energy theories with atomic physics experiments, the long-term vision being the extension to real-time quantum simulations of non-Abelian lattice gauge theories. 

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