Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L42: Advances in Analog Quantum SimulationFocus

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Sponsoring Units: GQI Chair: Phil Richerme, Indiana University Room: 389 
Wednesday, March 15, 2017 11:15AM  11:51AM 
L42.00001: Entanglement Generation and Area Law with LongRange Interactions Invited Speaker: Alexey Gorshkov In shortrange interacting systems, the speed at which entanglement can be established between two separated points is limited by a constant LiebRobinson velocity. This same limit also leads to the socalled arealaw bound on entanglement in onedimensional gapped shortrange interacting systems. In this talk, we will show that longrange interactions that decay with distance as a power law allow for faster entanglement generation and state transfer. We will also present sufficient conditions for the area law in gapped systems to hold even in the presence of longrange interactions. [Preview Abstract] 
Wednesday, March 15, 2017 11:51AM  12:03PM 
L42.00002: Towards a photonic Mott insulator in superconducting circuits Ruichao Ma, Clai Owens, Aman LaChapelle, Brendan Saxberg, David Schuster, Jonathan Simon Recent developments in circuit QED provide superconducting circuits as a unique platform for exploring quantum manybody phenomena with light. The absence of particle number conservation, however, makes creating and understanding of manybody photonic states challenging. Here we make a onedimensional lattice of coupled superconducting qubits with an additional pumping site and a lossy site incorporated at the end of the chain, which serves as an effective chemical potential for photons. When driven on the pumping site, the photons can spontaneously thermalize into the ground state of the lattice while the excess energy is dissipated via the lossy site. In the presence of strong photonphoton interaction via the qubit nonlinearity, we expect the creation of a Mott insulator state of light, which we can probe with temporal and spatiallyresolved measurements. These experiments will give insights to the microscopic investigation of nonequilibrium thermodynamics in stronglyinteracting quantum system, including the interplay between external driving and dissipation. [Preview Abstract] 
Wednesday, March 15, 2017 12:03PM  12:15PM 
L42.00003: Exploring the strongly driven spinboson model in the nonperturbative coupling regime using a superconducting circuit Pol FornDiaz, Luca Magazzu, Ron Belyansky, JeanLuc Orgiazzi, Ali Yurtalan, Borja Peropadre, Juan Jose GarciaRipoll, Milena Grifoni, Adrian Lupascu, Chris Wilson The spinboson model describes the interaction between a twolevel system and its environment, modeled as a bosonic bath. This model is particularly important in the study of decoherence, especially in solidstate qubits. Interestingly, when the interaction between the qubit and the environment crosses a threshold, the qubit dynamics cease to be dominated by coherent tunneling between its two eigenstates and transition into an incoherent tunneling regime. At stronger coupling, tunneling is quenched and the qubit wavefunction becomes localized. We have experimentally explored the transition from coherent to incoherent tunneling in the spinboson model using a superconducting flux qubit coupled to an open transmission line. A strong pump tone added to our probe reveals the internal dynamics of the system with the appearance of photonassisted tunneling resonances. We developed a theoretical model based on the noninteracting blip approximation (NIBA), which is in good agreement with our experimental observations. [Preview Abstract] 
Wednesday, March 15, 2017 12:15PM  12:27PM 
L42.00004: Dissipative phase transition in a onedimensional circuit QED lattice: Theory Andy C. Y. Li, Mattias Fitzpatrick, Neereja Sundaresan, Andrew Houck, Jens Koch Our theoretical and experimental work indicate the occurrence of a dissipative phase transition in a linear chain composed of coupled microwave resonators and superconducting qubits. Studies of circuit QED lattices, therefore, have great potential for advancing our understanding of nonequilibrium manybody physics of light. Motivated by the experimental results, we present theory investigating the physics of a driven damped circuitQED chain. Within meanfield approximation taking into account singlesite driving and finite size of the chain, we numerically explore basic features of the transition observed when increasing the drive strength beyond a critical threshold. [Preview Abstract] 
Wednesday, March 15, 2017 12:27PM  12:39PM 
L42.00005: Observation of a dissipative phase transition in a onedimensional circuit QED lattice Mattias Fitzpatrick, Neereja Sundaresan, Andy C.Y. Li, Jens Koch, Andrew Houck The building blocks of circuit QED provide a useful toolbox for the study of nonequilibrium and highly nonlinear behavior. Here, we present results from a onedimensional chain of 72 microwave cavities, each coupled to a superconducting qubit, where we coherently drive the system into a nonequilibrium steady state. We find experimental evidence for a dissipative phase transition in the system in which the steady state changes dramatically as the mean photon number is increased. Near the boundary between the two observed phases, the system demonstrates bistability, with characteristic switching times as long as 60 ms  far longer than any of the intrinsic rates known for the system. This experiment demonstrates the power of circuit QED systems for the studying nonequilibrium condensed matter physics and paves the way for future experiments exploring nonequilibrium physics with manybody quantum optics. [Preview Abstract] 
Wednesday, March 15, 2017 12:39PM  12:51PM 
L42.00006: Quantum simulations of a FermiHubbard model using a semiconductor quantum dot array Toivo Hensgens, Takafumi Fujita, Laurens Janssen, Xiao Li, Christian Reichl, Werner Wegscheider, Sankar Das Sarma, Lieven Vandersypen Quantum dots hold a promise for quantum simulations of highlycorrelated electronic phases as they readily adhere to a FermiHubbard model in the elusive stronginteraction, lowtemperature regime, where quantum correlations can span many sites. Working in solidstate inevitably entails disorder, however, which makes reaching homogeneity, even for small systems, rather difficult, and as such attempts at simulating FermiHubbard physics in solid state have been few and far between. We describe a toolbox for semiconductor quantum dots based on interpreting wellknown features in charge stability that allows for the independent tuning of sitespecific energy offsets and tunnel couplings, and use this to map out the accessible parameter space of a triple quantum dot device up to a total of 12 electrons and from $t/U=0.01$ to $t/U=0.12$. As tunnel couplings are homogeneously increased, we witness the delocalization transition from Coulomb blockade to collective Coulomb blockade, a finitesize analogue of the Mott metaltoinsulator transition. A further automated application of these ideas, on larger and more homogeneous samples, will make the synthesis of tailormade correlatedelectronic phases possible in the near future. [Preview Abstract] 
Wednesday, March 15, 2017 12:51PM  1:03PM 
L42.00007: Analog simulations of quantum impurity physics with a highimpedance Josephson transmission line Roman Kuzmin, Nicholas Grabon, YenHsiang Lin, Long Nguyen, Nitish Mehta, Vladimir Manucharyan Interacting 1D electrons are usually understood within the Luttinger liquid picture as noninteracting, acoustic excitations, analogous to TEM photons in a "telegraph"type transmission line. This system is known to exhibit nonperturbative, manybody dynamics upon introducing a single, backscattering impurity. The rich phenomenology of such system is usually referred to as quantum impurity physics. Interestingly, a backscattering impurity is mathematically equivalent to a Josephson junction embedded into a transmission line. The strong interaction regime (Luttinger parameter of order unity) occurs when the impedance of the transmission line is of the order of the resistance quantum. One can use this to probe quantum impurity physics in a simple, microwave scattering experiment. We present our implementation of a quantum impurity by introducing a small, "impurity" Josephson junction into a highimpedance transmission line made of moderate size junctions. [Preview Abstract] 
Wednesday, March 15, 2017 1:03PM  1:15PM 
L42.00008: Superconducting 3D Transmon Qubits for Analog Quantum Simulations Oscar Gargiulo, Stefan Oleschko, Phani Muppalla, Marcello Dalmonte, Peter Zoller, Gerhard Kirchmair We present an experimental investigation of the tunability of a 3D transmon qubit through the use of multiple magnetic fields. The 3D transmon is placed inside a copper cavity with sockets for coils and a hole for a magnetic hose. The magnetic hose is used to guide the magnetic field inside the cavity minimizing Eddy currents in the copper wall. As a first step we analyse the qubit tuning with static magnetic fields applied through the use of external coils. This allows us to set the qubit frequency to the desired bias point. Then we show that we can switch the magnetic field inside the cavity on fast time scales through the use of the magnetic hose. We also investigate the influence of the magnetic hose on the coherence time of the qubit. [Preview Abstract] 
Wednesday, March 15, 2017 1:15PM  1:27PM 
L42.00009: Detector Readout of Analog Quantum Simulators Iris Schwenk, Lin Tian, Michael Marthaler An important step in quantum simulation is to measure the manybody correlations of the simulated model. For a practical quantum simulator composed of a finite number of qubits and cavities, in contrast to manybody systems in the thermodynamic limit, a measurement device can generate strong backaction on the simulator, which could prevent the accurate readout of the correlation functions. Here we calculate the readout of a detector coupled to analog quantum simulators. We show that reliable characterization of the manybody correlations of the simulators can be achieved when the coupling operators obey the Wick’s theorem. Our results are illustrated with two examples: a simulator for an harmonic oscillator and a simulator for the free electron gas. We also present a method, which under certain constraints, allows for the reconstruction of the ideal correlators from the measurements on a perturbed quantum simulator. [Preview Abstract] 
Wednesday, March 15, 2017 1:27PM  1:39PM 
L42.00010: Analog quantum simulation of the Rabi model in the ultrastrong coupling regime Jochen Braum\"uller, Michael Marthaler, Andre Schneider, Alexander Stehli, Hannes Rotzinger, Martin Weides, Alexey V. Ustinov The quantum Rabi model describes the fundamental mechanism of lightmatter interaction. It consists of a twolevel atom or qubit coupled to a quantized harmonic mode via a transversal interaction. In the weak coupling regime, a rotating wave approximation can be applied and the quantum Rabi Hamiltonian reduces to the wellknown JaynesCummings Hamiltonian. In the ultrastrong coupling regime, where the effective coupling strength $g$ is comparable to the energy $\omega$ of the bosonic mode, the counter rotating terms can no longer be neglected, revealing remarkable features in the system dynamics. Here, we demonstrate an analog quantum simulation of the quantum Rabi model in the ultrastrong and close deep strong coupling regime. The quantum hardware of the simulator is a superconducting circuit embedded in a cQED setup. The simulation scheme is based on the application of two classical transversal microwave drive pulses used to engineer the desired effective Hamiltonian. We observe a fast quantum state collapse followed by periodically recurring quantum revivals of the initial qubit state, which is the most distinct signature of the synthesized model. We achieve a relative coupling ratio of $g/\omega \sim 0.7$, approaching the deep strong coupling regime. [Preview Abstract] 
Wednesday, March 15, 2017 1:39PM  1:51PM 
L42.00011: Exploring Ultrastrong Coupling Effects Using a Josephson Mixer Danijela Marković We use the Josephson Ring Modulator (JRM) to demonstrate new signatures of the ultrastrong coupling between two bosonic modes. The JRM implements a three wave mixer between two microwave modes $a$ and $b$. When pumping the JRM at a red (blue) frequency $f_R^{(0)}=f_af_b$ ($f_B^{(0)}=f_a+f_b$), we realize frequency conversion between modes at a rate $G_R$ (two mode squeezing at a rate $G_B$). The effective ultrastrong coupling is obtained when the JRM is pumped by these two tones simultaneously so that $G_B=G_R$ is larger than the relaxation rate of the modes $a$ and $b$. We reach this regime by weakly coupling the modes of a Josephson mixer to measurement transmission lines compared to the rates $G_{B,R}$. By detuning the blue pump at a frequency $f_B=f_B^{(0)}+2\delta$, two peaks appear in the spectral density of each mode output, separated by $2\delta$. A key signature of ultrastrong coupling corresponds to the splitting of each of these peaks in two other peaks whose separation is set by $G_R$. We present preliminary experimental results that demonstrate this behavior and reach the regime where a strong (20~dB) peak appears in the spectral density of each mode output at $G_R=G_B=\delta/2$. We should be able to demonstrate both twomode and single mode squeezing. [Preview Abstract] 
(Author Not Attending)

L42.00012: What is the effect of decoherence on an analog quantum simulator? Sebastian Zanker, Jan Reiner, Iris Schwenk, Juha Leppäkangas, Michael Marthaler Simulation of interacting electron systems is one of the great challenges of modern quantum chemistry and solid state physics. Controllable quantum systems offer the opportunity to create artificial structures which mimic the properties of a quantum system of interest. An interesting quantity to extract is the spectral function. We study a system of coupled qubits which can be mapped to the fermionic model of interest and discuss, how the coupling of qubits to sources of decoherence can be transformed to a fermionic model using the same mapping. In the spectral function only features larger than the single qubit decoherence rate can be resolved, which we quantify using the fermionic mapping and a diagrammatic approach on Keldysh contour. For simple systems we compare master equation calculations to our more general approach. [Preview Abstract] 
Wednesday, March 15, 2017 2:03PM  2:15PM 
L42.00013: Reliability of analog quantum simulation Mohan Sarovar, Jun Zhang, Lishan Zeng Analog quantum simulators (AQS) will likely be the first nontrivial application of quantum technology for predictive simulation. However, there remain questions regarding the degree of confidence that can be placed in the results of AQS since they do not naturally incorporate error correction. We formalize the notion of AQS reliability to calibration errors by determining sensitivity of AQS outputs to underlying parameters, and formulate conditions for robust simulation. Our approach connects to the notion of parameter space compression in statistical physics and naturally reveals the importance of model symmetries in dictating the robust properties. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multimission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the United States Department of Energy's National Nuclear Security Administration under Contract No. DEAC0494AL85000. [Preview Abstract] 
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