Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V28: Superconducting Qubit Systems IIILive
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Sponsoring Units: DQI Chair: Leonardo Ranzani, BBN Technology - Massachusetts |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V28.00001: Scalable multiphoton generation from cavity-synchronized single-photon sources Ming Li, Juan Jose Garcia-Ripoll, Tomas Ramos We propose an efficient, scalable and deterministic scheme to generate up to hundreds of indistinguishable photons over multiple channels, on demand. Our design relies on multiple single-photon sources, each coupled to a waveguide, and all of them interacting with a common cavity mode. The cavity synchronizes and triggers the simultaneous emission of one photon by each source, which are collected by the waveguides. For a state-of-the-art circuit QED implementation, this scheme supports the creation of single photons with purity, indistinguishability, and efficiency of 99% at rates of ∼MHz. We also discuss conditions to create a device to produce 30-photon simultaneously with efficiency above 70% at a rate of hundreds of kHz. This is several orders of magnitude more efficient than previous demultiplexed sources for boson sampling, and enables the realization of deterministic multi-photon sources and scalable quantum information processing with photons. [See arXiv:2009.02382] |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V28.00002: Spectroscopic Observation of Crossover from Classical Duffing Oscillator to Kerr Parametric Oscillator Tomohiro Yamaji, Sota Kagami, Aiko Yamaguchi, Tetsuro Satoh, Kazuki Koshino, Hayato Goto, Zhirong Lin, Yasunobu Nakamura, Tsuyoshi Yamamoto A Kerr parametric oscillators (KPO) is a parametric oscillator in the single-photon Kerr regime, where the Kerr nonlinearity is larger than the photon loss rate (but not as large as transmon qubits). This regime is relatively unexplored, and the KPOs have a wide range of potential applications such as deterministic generation of Schrödinger cat state [1] and quantum computation [2]. We study microwave response of a Josephson parametric oscillator consisting of a superconducting transmission-line resonator with an embedded dc-SQUID. The dc-SQUID allows to control the magnitude of a Kerr nonlinearity over the ranges where it is smaller or larger than the photon loss rate. Spectroscopy measurements reveal the change of the microwave response from a classical Duffing oscillator to a Kerr parametric oscillator in a single device. In the single-photon Kerr regime, we observe parametric oscillations with a well-defined phase of either 0 or π, whose probability can be controlled by an externally injected signal. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V28.00003: From quantum circuit refrigeration to lasing: master equation approach Hao Hsu Recently, a “quantum circuit refrigerator” (QCR) consisting of a voltage biased superconductor–insulator–normal-metal–insulator–superconductor (SINIS) tunnel junction has been experimentally demonstrated to cool superconducting resonators [1], in agreement with theoretical expectations [2]. Theory also predict that the QCR can reset superconducting qubits fast and accurately [3]. Here we discuss a master equation approach to the dynamics of a QCR coupled to a two-level system. We find that the time evolution of the distribution function for the charge on the normal metal is slow on the scale of the qubit reset time; therefore, one can neglect the charge dynamics when calculating the reset time, validating the assumptions in Refs. [2, 3]. Replacing the normal-metal island with a quantum dot, we find an operation regime where the photon-assisted tunneling can serve as a pumping mechanism. Using our master equation approach, we investigate the possibility of lasing by coupling the quantum dot QCR to a resonator. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V28.00004: Digital-Analog Quantum Simulations Using The Cross-Resonance Effect Tasio Gonzalez-Raya, Rodrigo Asensio-Perea, Ana Martin, Lucas Chibebe Céleri, Mikel Sanz, Pavel Lougovski, Eugen Dumitrescu Digital-analog quantum computation aims to reduce the resource requirements needed for quantum information processing by augmenting circuits with transformations generated from a system’s underlying Hamiltonian. We consider an extension of the cross-resonance effect, up to first order in the drive amplitude over detuning, from a pair of qubits to 1D chains and 2D lattices. In an appropriate reference frame, we find a two-local Hamiltonian comprised of non-commuting interactions. Augmenting the analog dynamics with single-qubit gates, we generate families of analog Hamiltonians. Toggling between these Hamiltonians, we design sequences simulating the dynamics of Ising, XY, and Heisenberg models. Our 1D Ising and XY sequences are Trotter error-free and we also show that the Trotter errors for 2D XY and 1D Heisenberg chains are reduced, with respect to a digital decomposition, by a constant factor. Our Hamiltonian toggling techniques could be extended to derive new Hamiltonians which may be of use in more complex digital-analog quantum simulations for various models. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V28.00005: Probing Multi-Site Correlators in a Bose Hubbard lattice Brendan Saxberg, Gabrielle Roberts, Andrei Vrajitoarea, Margaret Panetta, Ruichao Ma, David I Schuster, Jon Simon Strongly-correlated quantum materials can be studied synthetically using the flexible toolset of microwave photons and superconducting circuits in the circuit QED paradigm. We build a 1D Bose-Hubbard lattice for photons where capacitively coupled transmon qubits serve as lattice sites, and the transmon anharmonicity corresponds to strong photon-photon collisions. In previous work, we employed an engineered reservoir to realize a dissipatively stabilized site and couple it to the lattice to prepare a n=1 Mott insulator. Recent improvements to our experiment will allow us to probe multi-site correlations. We discuss prospects for preparing and probing superfluids, and exploring the response of quantum fluctuations in the presence/absence of the stabilizer. These efforts can shed light on the intricate interplay of correlations, entanglement and thermalization in these driven-dissipative systems. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V28.00006: Photon decay in circuit QED as a new resource for quantum impurity simulations Roman Kuzmin, Nicholas Grabon, Nitish Mehta, Amir Burshtein, Moshe Goldstein, Vladimir Manucharyan We present a new approach to analog simulations of quantum impurity problems in circuit QED. Our approach relies on the phenomenon of single photon decay, which is the decay of a microwave photon into lower energy photons driven by a local quantum non-linearity (impurity) [1, 2]. Although there is no practical analog for a single photon decay in traditional quantum optics, this phenomenon is ubiquitous in the bosonic description of strongly-correlated 1D systems, which is at the heart of the modern understanding of strongly-correlated phenomena. Therefore, photon lifetime data represents the outcome of a non-trivial quantum simulation. As a specific example, we built a system consisting of a weak Josephson junction galvanically embedded into a long section of a high-impedance transmission line. By measuring the photon decay rates and comparing them to a newly developed theoretical model, we successfully verified the simulation outcome in the parameter regime accessible to analytical calculations. Changing the impurity circuit allows us to simulate such important phenomena as electron tunneling in Luttinger liquids and dissipative phase transitions, as well as Kondo physics in and out of equilibrium. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V28.00007: Large fluctuations of T1 in long-lived transmon qubits Kungang Li, Sudeep Dutta, Rui Zhang, Zachary Steffen, Dylan Poppert, Jeffrey Bowser, Shahriar Keshvari, Benjamin Palmer, Christopher J Lobb, Frederick C Wellstood Recently the relaxation time T1 of transmons has increased, as has the size of the fluctuations in T1. To investigate the source of these fluctuations, we measured the T1 of transmons made with an electrode layer of pure aluminum and a counter-electrode layer made with either pure Al or oxygen-doped granular Al. The superconducting energy gap of the counter-electrode depends on the grain size, which depends on the oxygen doping as well as the layer thickness. At 20 mK, an oxygen-doped device showed T1 variations between about 80 and 300 μs, while an un-doped device on the same chip showed uncorrelated T1 variations between 50 and 100 ms. Measurements of the fluctuations versus temperature reveal that the standard deviation of T1 is proportional to T1, even above 150 mK, where the transmon relaxation is dominated by thermally-generated quasiparticles. We discuss why this behavior is not consistent with the two most commonly proposed mechanisms, fluctuations in two-level-system dielectric loss and fluctuations in the density of non-equilibrium quasiparticles, and propose an alternative mechanism that is consistent with the observed behaviors. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V28.00008: Deterministic Generation of Multipartite-Entangled Microwave Photonic States Jean-Claude Besse, Kevin Reuer, Michele Collodo, Arne Wulff, Lucien Wernli, Adrian Espinosa Copetudo, Daniel Malz, Paul Magnard, Abdulkadir Akin, Mihai Gabureac, Graham J. Norris, Juan Ignacio Cirac, Andreas Wallraff, Christopher Eichler Sources of entangled electromagnetic radiation are a key component for distributed quantum information processing, metrology, and the study of quantum many-body physics. Generation of multi-mode entangled states of radiation with a large entanglement length, that is neither probabilistic nor restricted to generate specific types of states, remains challenging. Here, we demonstrate a unique superconducting device able to deterministically generate a wide family of entangled states of microwave radiation such as cluster, GHZ, and W states [1]. We tomographically reconstruct all quantum many-body states entirely for up to N = 4 photonic modes and characterize states for larger N by considering the repetitive nature of the sequential emission process. We estimate that localizable entanglement persists over a distance of approximately ten photonic qubits. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V28.00009: Ground state of open circuit QED systems in the deep-strong coupling regime Tomohiro Shitara, Motoaki Bamba, Fumiki Yoshihara, Tomoko Fuse, Sahel Shafiq Ashhab, Kouichi Semba, Kazuki Koshino We investigate theoretically how the ground state of a qubit-resonator system in the deep-strong coupling regime is affected by the coupling to an environment. We show that the state of the qubit-resonator system strongly depends on the nature of the resonator-waveguide and resonator-qubit coupling, i.e., capacitive or inductive. When the resonator couples to the qubit and the environment in different ways (e.g., one is inductive and the other is capacitive), the system is almost unaffected by the resonator-waveguide coupling. In contrast, when the couplings are of the same type (e.g., both are inductive), the average number of virtual photons increases and the quantum superposition realized in the qubit-resonator entangled ground state is partially degraded due to the resonator-waveguide coupling. In this case, since the superposition becomes more fragile when the qubit-resonator coupling strength gets large, there exists an optimal strength of the qubit-resonator coupling to maximize the nonclassicality of the qubit-resonator system in a realistic setup. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V28.00010: True photon blockade effects with arbitrarily weak nonlinearities Andrew Lingenfelter, David Roberts, Aashish Clerk Photon blockade is a paradigmatic effect where strongly driving a nonlinear photonic cavity results in a highly non-classical state exhibiting a sharp cut-off in its photon number distribution. Such states are a resource for a variety of different quantum information processing tasks. Unfortunately, the standard blockade mechanism requires extremely strong nonlinearities: they must exceed loss rates even at the few photon level. Recently an unconventional photon-blockade effect was introduced that only requires weak nonlinearities [1]. However this mechanism does not result in a sharp photon-number cutoff, and is limited to producing Gaussian states [2]. Here, we discuss and analyze an alternate route to photon blockade that also requires very weak nonlinearities, but is capable of generating highly non-Gaussian states that have a sharp photon-number cut-off. We show how our scheme can be implemented using a rather generic setup of a driven cavity mode with a Kerr (i.e Hubbard-U) type nonlinearity. Our scheme is compatible both with a variety of quantum optics platforms, as well as circuit QED setups. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V28.00011: Towards a 4-local coupler for superconducting flux qubits – Part 1: Quantum landscape engineering of the ground state Tim Menke, Cyrus Hirjibehedin, Steven Weber, Jochen Braumüller, Antti Vepsäläinen, Roni Winik, Gabriel O Samach, David K Kim, Alexander Melville, Bethany Niedzielski, Danna Rosenberg, Mollie Schwartz, Jonilyn Yoder, Simon Gustavsson, Andrew James Kerman, William Oliver The response of a superconducting circuit's ground state energy to external flux is a versatile resource for qubit architecture design. For instance, it can be engineered to mediate interactions between flux qubits or assist in qubit readout. Here we propose a methodology for adding higher-order polynomial terms into the flux dependence of the circuit ground state by strongly coupling a series of rf SQUIDs, thereby landscaping the spectrum at the fluxon level. The operation principle of such a circuit module is demonstrated experimentally. We find that it has the desired spectral property and does not adversely affect the lifetime of a connected flux qubit. It is thus suitable as a quantum coupling or readout module. In addition, we numerically show that the spectral landscaping concept can be scaled by systematically adding circuit loops to the module. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V28.00012: Towards a 4-local coupler for superconducting flux qubits - part 2: distinguishing multi-spin interactions from lower-order effects Thomas Bergamaschi, Tim Menke, Cyrus Hirjibehedin, Steven Weber, Andrew James Kerman, William Oliver Many-local coupling can be effectively achieved with artificial quantum spins but is challenging to verify experimentally. Here we present a method to characterize many-local interactions by analyzing the variation of the system’s spectral gap with the local spin fields. By using generally accessible measurement techniques, we numerically simulate experimental quantification of many-local interactions. These interactions are shown to be distinguishable from lower-order contributions, which demonstrates that the method enables robust exploration of many-local interactions across a broad range of coupling strengths and can be implemented for a variety of qubit modalities. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V28.00013: Ultrastrong light-matter interaction in a photonic crystal waveguide Andrei Vrajitoarea, Ron Belyansky, Rex Lundgren, Seth P Whitsitt, Alexey V Gorshkov, Andrew Houck Superconducting circuits have emerged as a rich platform for emulating synthetic quantum materials composed of artificial atoms and photonic lattices. Here, we apply this toolbox for exploring the physics of a quantum impurity coupled to the many modes of a photonic crystal. In previous experiments, strongly coupling a transmon qubit to the band structure of a stepped impedance waveguide has led to the first observation of atom-photon dressed bound states. In this work, we push the coupling strength even further to go beyond the single-photon limit. Our platform consists of a fluxonium qubit galvanically coupled to a linear chain of coupled microwave resonators. Probing transport through the waveguide reveals that the propagation of a single photon becomes a many-body problem as multi-photon bound states participate in the scattering dynamics. Furthermore, we study the effective photon-photon interactions induced by the impurity by probing the inelastic scattering spectrum. The measured correlations in the emitted quadrature fields at each waveguide mode reveal signatures of multi-mode entanglement. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V28.00014: Dynamics of Coupled Hodgkin-Huxley Quantum Neurons Tasio Gonzalez-Raya, Mikel Sanz The Hodgkin-Huxley model describes the conduction of nervous impulses, realized by flows of different ionic species through the axon’s membrane, through a circuit featuring ionic conductances that depend on previous depolarizing voltages. This circuit, projected in the quantum realm [1,2], consists of a capacitor and a quantum memristor, that describe the axon membrane’s charging capacity and voltage-dependent memory response, respectively. We consider the connection of two such circuits in parallel, subjected to a quantized input source as a resonator capacitively coupled to the circuit [2], and study the dynamical system and the quantum correlations that arise between the two circuits. Since the main quantum contribution on these systems comes from the second moment of the voltage [1], we will investigate correlations such as degree of coherence, between voltage and conductance in both circuits, proving that these are quantum variables. This study paves the way for hardware-based neuromorphic quantum computing, as well as quantum machine learning, which might be more efficient resource-wise. |
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