Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E26: Driven and Dissipative Superconducting CircuitsFocus

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Sponsoring Units: DQI Chair: Shyam Shankar, Yale Univ Room: BCEC 160B 
Tuesday, March 5, 2019 8:00AM  8:12AM 
E26.00001: Observation of the paritytime symmetry breaking transition in a dissipative superconducting qubit Mahdi Naghiloo, Maryam Abbasi, Yogesh N Joglekar, Kater Murch NonHermitian systems that exhibit paritytime (PT) symmetry have been recently studied in electrical, optical, and mechanical classical systems revealing applications in nonreciprocal devices and sensing. While questions have remained as to whether PTsymmetric systems are realizable in the quantum regime due to the role of quantum noise in amplifiers, the topological features associated with PTsymmetric Hamiltonians are shared by dissipative systems with selective losses, which can be realized at the quantum level. We employ bath engineering techniques to realize a nonHermitian Hamiltonian that has effective PT symmetry for a superconducting circuit. We use quantum state tomography to observe the PT symmetry breaking transition as manifested in the evolution of both diagonal and offdiagonal elements of the qubit density matrix 
Tuesday, March 5, 2019 8:12AM  8:24AM 
E26.00002: An experimental implementation for stabilizing Schrödinger cat states in a Kerr nonlinear resonator  Basic concepts Nicholas Frattini, Alexander Grimm, Shantanu O. Mundhada, Shruti Puri, Steven Touzard, Mazyar Mirrahimi Schrödinger cat states of microwave light based on superpositions of coherent states in a superconducting resonator can be used as errorprotected qubits as well as auxiliary systems for faulttolerant quantum computation. It has recently been shown that such states can be stabilized by applying a twophoton drive to a Kerr nonlinear resonator. In this talk, we will give an introduction on this type of qubit and its potential uses in quantum computation before discussing an experimental implementation. Our system is based on a modified, lowanharmonicity, transmon qubit. Instead of a Josephson junction, we use a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) providing us with both three and fourwavemixing terms. This simultaneously implements the required nonlinearity and gives us access to a strong twophoton drive. We will report on the details of this implementation and present our progress towards the realization of this stabilization scheme. Part one of this twopart presentation will introduce the basic concept of this qubit and its uses in quantum information. 
Tuesday, March 5, 2019 8:24AM  8:36AM 
E26.00003: An experimental implementation for stabilizing Schrödinger cat states in a Kerr nonlinear resonator  Part 2: Experiment. Alexander Grimm, Nicholas Frattini, Shantanu O. Mundhada, Shruti Puri, Steven Touzard, Mazyar Mirrahimi, Shyam Shankar, Michel H. Devoret Schrödinger cat states of microwave light based on superpositions of coherent states in a superconducting resonator are useful as errorprotected qubits as well as auxiliary systems for faulttolerant quantum computation. It has recently been shown that such states can be stabilized by applying a twophoton drive to a Kerr nonlinear resonator. In this talk, we will give an introduction on this type of qubit and its potential uses in quantum computation before discussing an experimental implementation of this idea. Our system is based on a modified, lowanharmonicity, transmon qubit. Instead of a Josephson junction, we use a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) providing us with both three and fourwavemixing terms. This simultaneously realizes the required nonlinearity and gives us access to a strong twophoton drive. We report on this implementation and present preliminary results towards the realization of a stabilization scheme. 
Tuesday, March 5, 2019 8:36AM  8:48AM 
E26.00004: Directional Quantum State Transfer by Dissipation I – Conceptual Overview Chen Wang, Jeffrey Gertler Quantum state transfer from an informationcarrying qubit to a receiving qubit is ubiquitous for quantum information technology. In a closed quantum system, this task requires preciselytimed control of coherent qubitqubit interactions that are intrinsically reciprocal. Here, breaking reciprocity by dissipation in an open system, we propose a type of cascaded quantum systems where a quantum state can be spontaneously transferred between stationary qubits without timedependent control. We show that the minimum system dimension for transferring one qubit of information in this way is 3x2 (between one physical qutrit and one physical qubit), plus one auxiliary reservoir. We discuss general requirements and strategies for such autonomous quantum state transfer as well as its connection with autonomous quantum error correction. We further discuss physical implementation schemes, with our experimental progress in a superconducting circuit QED platform to be described in a following presentation. 
Tuesday, March 5, 2019 8:48AM  9:00AM 
E26.00005: Directional Quantum State Transfer by Dissipation II – Implementation in Circuit QED Jeffrey Gertler, Chen Wang, Xiaowei Deng Dissipation is a remarkable resource in quantum information processing that can be used to stabilize and manipulate quantum states or manifolds. Here we utilize dissipation to implement an autonomous technique for quantum state transfer, with builtin directionality, that eliminates the need for time dependent external control. We report experimental progress towards this state transfer in a 3D superconducting circuit QED system between a threelevel transmon (Alice) and a coaxial storage cavity (Bob). The quantum state is irreversibly transferred from Alice to Bob via dissipation of a coupled axillary transmon reservoir, activated by two fourwave mixing processes produced by offresonant drives. Using virtual states of the reservoir to compensate for unwanted dispersive frequency shift, we show that quantum coherence can be maintained throughout the dissipative process, leading to highfidelity state transfer which is limited by inherent qubit/cavity decoherence. 
Tuesday, March 5, 2019 9:00AM  9:12AM 
E26.00006: Reconstructing Josephson CurrentPhase Relations with Intermodulation Spectroscopy Shan Jolin, Thomas Weißl, Riccardo Borgani, David Haviland

Tuesday, March 5, 2019 9:12AM  9:24AM 
E26.00007: Dissipationfree nonHermitian physics using quantum parametric amplifiers Yuxin Wang, Aashish Clerk There has been considerable interest in drivendissipative systems governed by nonHermitian effective Hamiltonians. These systems can exhibit a range of unusual phenomena, such as the spontaneous breaking of paritytime (PT) symmetry [1], and chiral effects associated with encircling exceptional points [1]. Quantum versions of these effects are however often compromised by their dissipative nature. Here, we show that many of these nonHermitian effects can be realized in a completely nondissipative setting, by exact unitary mappings to parametricallydriven bosonic setups. Applications of these mappings include enhanced quantum sensing using exceptional points, and chiral switching based on encircling of exceptional points. Our approach could be implemented experimentally using superconducting quantum circuits, or in optomechanical systems. 
Tuesday, March 5, 2019 9:24AM  9:36AM 
E26.00008: Driven Kerr resonators: new regimes of solvability and quantum bistability David Roberts, Aashish Clerk The driven Kerr resonator is one of the most iconic solvable models in cavity QED [1]. When subject to twophoton (parametric) driving it can exhibit bistability, something that has been exploited in several recent experiments in circuit quantum electrodynamics and proposals for protected quantum memories [2, 3]. Here, we develop a more physically transparent method for finding analytic solutions to driven Kerr resonators. This allows us to solve for a wider class of systems than in previous work, and also allows us to derive closedform expressions for steadystate Wigner functions. More intriguingly, our approach also uncovers a new class of previouslyoverlooked points of quantum bistability in the resonator's phase diagram. Our work could open up new avenues for using nonlinear driven superconducting quantum circuits as quantum processors. 
Tuesday, March 5, 2019 9:36AM  9:48AM 
E26.00009: Suppressing the instabilities of the RF driven transmon by a kinetic inductive shunt  Part 1: Motivation and modelization Jayameenakshi Venkatraman, Xu Xiao, Clarke Smith, Zaki Leghtas, Lucas Verney, Mazyar Mirrahimi, Shyam Shankar, IoanMihai Pop, Michel H. Devoret The transmon is ubiquitous in circuit QED experiments due to its remarkable coherence properties and simplicity of design and fabrication. However, when strongly driven at microwave frequencies, the transmon exhibits various kinds of instabilities. FloquetMarkov theory indeed predicts such instabilities. Shunting the transmon with a linear inductance qualitatively changes the potential seen by the phase, thus increasing the device stability under certain conditions. We call the resulting qubit the inductivelyshunted transmon (IST) to distinguish it from the RF SQUID. Comparison of driven transmons and ISTs with different implementations offers insights in eliminating these instabilities, and also sheds light on the fundamental problem of chaos in a strongly driven dissipative quantum system. This talk will focus on the motivation and modelization. 
Tuesday, March 5, 2019 9:48AM  10:24AM 
E26.00010: Quantum Electrodynamic Modeling of Superconducting Circuits Invited Speaker: Hakan Tureci The demand for rapid and highfidelity execution of initialization, gate and readout operations casts tight constraints on the accuracy of quantum electrodynamic modeling of superconducting integrated circuits. Attaining the required accuracies requires reconsidering our basic approach to the quantization of the electromagnetic field in spatially inhomogeneous waveguides and the notion of normal modes. I will discuss a computational framework based on the HeisenbergLangevin approach to address these fundamental questions. This framework allows the accurate determination of the quantum dynamics of a superconducting qubit in an arbitrarily complex electromagnetic environment infinite in extent, for any coupling strength and any degree of openness. This includes the regime of overlapping resonances and the "ultrastrong coupling" regime. I will also discuss the effectiveness of this computational approach in meeting the demands of presentday quantum computing research. 
Tuesday, March 5, 2019 10:24AM  10:36AM 
E26.00011: Suppressing the instabilities of RF driven transmon by a kinetic inductive shunt  Part 2: Experimental results Xu Xiao, Jayameenakshi Venkatraman, Clarke Smith, Zaki Leghtas, Lucas Verney, Mazyar Mirrahimi, Shyam Shankar, IoanMihai Pop, Michel H. Devoret The transmon is ubiquitous in circuit QED experiments due to its remarkable coherence properties and simplicity of design and fabrication. However, when strongly driven at microwave frequencies, the transmon exhibits various kinds of instabilities. FloquetMarkov theory indeed predicts such instabilities. Shunting the transmon with a linear inductance qualitatively changes the potential seen by the phase, thus increasing the device stability under certain conditions. We call the resulting qubit the inductivelyshunted transmon (IST) to distinguish it from the RF SQUID. Comparison of driven transmons and ISTs with different implementations offers insights in eliminating these instabilities, and also sheds light on the fundamental problem of chaos in a strongly driven dissipative quantum system. This talk will focus on recent experimental results for such investigations. 
Tuesday, March 5, 2019 10:36AM  10:48AM 
E26.00012: Bistability and Critical Slowing Down in Superconducting Circuits Paul Brookes, Giovanna Tancredi, Themis Mavrogordatos, Andrew D Patterson, Joseph Rahamim, Martina Esposito, Peter Leek, Eran Ginossar, Marzena Hanna Szymanska We carry out an experimental and numerical examination of bistability and critical slowing down in the strongly driven nonlinear regime of circuit QED. The system under study is a 3D microwave cavity coupled to a transmon qubit. By measuring the response of the cavity to a step function drive pulse, we see that in the bistable regime the time required for the system to reach equilibrium is far longer than both the cavity and qubit relaxation times. We observe that this equilibration time saturates at high drive powers. Through careful modelling we are able to attribute this saturation to phase noise of the transmon. In addition we demonstrate that the equilibration time is highly sensitive to the temperature of the cavity. 
Tuesday, March 5, 2019 10:48AM  11:00AM 
E26.00013: Measurement of the Crossover from Photon Ordering to Delocalization in a DrivenDissipative Superconducting Resonator System Michele Collodo, Anton Potocnik, Simone Gasparinetti, JeanClaude Besse, Marek Pechal, Mahdi Sameti, Michael J. Hartmann, Andreas Wallraff, Christopher Eichler Sizeable photonphoton interactions in networks of nonlinear oscillators enable the study of strongly correlated photons in nonequilibrium quantum manybody systems. We present a system composed of two superconducting resonators, coupled nonlinearly by a superconducting quantum interference device (SQUID). By applying a parametrically modulated magnetic flux we control the linear photon hopping rate between the two resonators and its ratio with the crossKerr rate. When increasing the hopping rate we observe a fully controllable crossover in the spatial correlations of the photonic fields of the two resonators, from photon selfordering to delocalization of photons. The presented parametric coupling scheme is intrinsically robust to frequency disorder and may therefore prove useful for realizing largerscale resonator arrays, and in turn facilitate active control of extended correlated quantum gases for the purpose of emulating other less accessible quantum systems. 
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