Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y33: Superconducting Circuits: General |
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Sponsoring Units: DQI Chair: Ben Palmer, University of Maryland, Laboratory for Physical Sciences Room: LACC 408B |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y33.00001: Inversions of qubit energy levels in deep-strongly-coupled qubit-oscillator circuits Fumiki Yoshihara, Tomoko Fuse, Ziqiao Ao, Sahel Ashhab, Kosuke Kakuyanagi, Shiro Saito, Takao Aoki, Kazuki Koshino, Kouichi Semba The electromagnetic field inside a cavity renormalizes the transition frequency of an atom inside the cavity. The Lamb (n = 0) and n-photon ac-Stark shifts can be written as Δ - Δ_{n}, where Δ and Δ_{n} are respectively the transition frequencies of a non-interacting and renormalized atom. In the limit of Δ « ω, where ω is the resonance frequency of the cavity, Δ_{n} can be written as [1] Δ_{n}/Δ = exp[-2(g/ω)^{2}]L_{n}[(2g/ω)^{2}], where g is the coupling constant between the atom and the electromagnetic field in the cavity and L_{n} is a Laguerre polynomial. This equation indicates that Δ_{n} changes sign when L_{n} crosses zero; the atom's ground and excited states are “inverted”. We use circuits of a flux qubit deep-strongly coupled to an LC oscillator [2], where g ≈ ω. The experimentally observed qubit frequencies Δ_{n} (n = 0, 1, 2) were very close to those given by the equation above. [1] S. Ashhab and F. Nori, PRA 81, 052311 (2010). [2] F. Yoshihara, T. Fuse et al., Nat. Phys. 13, 44 (2017). |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y33.00002: A compact 3D quantum memory Frank Deppe, Edwar Xie, Daniel Repp, Peter Eder, Michael Fischer, Jan Goetz, Stefan Pogorzalek, Kirill Fedorov, Achim Marx, Rudolf Gross Superconducting qubits coupled to rectangular 3D cavity resonators exhibit coherence times on the order of a few tens of microseconds. In practice, one simultaneously couples the qubit to an even longer-lived memory cavity and low-quality readout cavity. The physical dimensions of such an device can be significantly reduced by integrating both functionalities into a single multimode cavity. Here, we engineer the fundamental and the first harmonic mode of a rectangular aluminum cavity in such a way, that the former one couples well to the external feedline, whereas the latter one does not. A transmon qubit couples to both modes with a rate g/2π=60 MHz. We store qubit states in the memory using a second-order protocol, observing a lifetime enhancement by a factor of 7.2. At the same time, the readout of our qubit is approximately 120 times faster than the storage time. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y33.00003: Period-Tripling Subharmonic Oscillations in a Driven Superconducting Resonator Ida-Maria Svensson, Andreas Bengtsson, Philip Krantz, Jonas Bylander, Vitaly Shumeiko, Per Delsing We have observed period-tripling subharmonic oscillations in a driven superconducting coplanar waveguide resonator operated in the quantum regime, k_{B}T << hω/2π. The resonator is terminated by a tunable inductance that provides a Kerr-type nonlinearity. We detected the output field quadratures at frequencies near the fundamental mode, ω/2π ∼ 5 GHz, when current driving the resonator with an external signal at 3ω, with amplitude exceeding an instability threshold. We observed three stable radiative states with equal amplitudes, phase-shifted by 2π/3 radians, red-detuned from the fundamental mode. The downconversion from 3ω to ω is strongly enhanced by near-resonant excitation of the second mode of the resonator, and the cross-Kerr effect. Our experimental results are in quantitative agreement with a model for the driven dynamics of two coupled modes. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y33.00004: Quantum state tomography of three-photon down conversion in a superconducting circuit Isaac Fernando Quijandria Diaz, Ingrid Strandberg, Göran Johansson <!--StartFragment-->Circuit QED has proven to be a platform which offers possibilities for realizations beyond the scope of quantum optics. In particular, fast modulation of a boundary condition in the 1D field propagating through a transmission line has been employed for a realization of the dynamical Casimir effect. A remarkable advantage over quantum optics setups are effective photon-photon interactions engineered via a Josephson junction or a SQUID. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y33.00005: Multi-photon Transitions in an Anharmonic Quantum Oscillator: Probing the AC Stark Shifts of Higher Levels under Field Drive Andre Schneider, Patrizia Stehle, Jochen Braumüller, Hannes Rotzinger, Lingzhen Guo, Michael Marthaler, Alexey Ustinov, Martin Weides We report on the investigation of a superconducting anharmonic multi-level circuit under the influence of a detuned and strong microwave drive. We observe the AC-Stark shift of the transition frequencies caused by the applied drive and demonstrate that this shift depends on the anharmonicity, the drive amplitude and the detuning between drive and transition frequency. For large detunings we find the shift to be linear to the power of the drive, whereas for small detunings, a more complex expression for the individual transitions is calculated. Experimentally, multi-photon transitions via virtual energy levels of our system up to the third excited state are studied and shifts larger than the anharmonicity of the system are observed. The measured AC-Stark shift of higher order multi-photon transitions under increasing drive amplitude is demonstrated to be in good agreement with the analytic model and numerical simulations. |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y33.00006: Emergent Dynamics of Noise and Loss-Generating Paramagnetic Spins in Superconducting Circuits Keith Ray, Nicholas Materise, Jonathan DuBois, Vincenzo Lordi The emergent mesoscale dynamics of noise and loss-generating degrees of freedom in superconducting qubits, such as surface adsorbates, defects, and impurities, ultimately determine the dynamics of the qubit. Paramagnetic O_{2} has been identified experimentally as a likely flux noise source [Phys. Rev. Applied 6, 041001 (2016)], as well as atomic hydrogen [Phys. Rev. Lett. 118, 057703 (2017)]. In addition, computational studies [PRL 112, 017001 (2014)] of magnetic spins induced by molecules adsorbed on bare Al-terminated Al_{2}O_{3} demonstrated the possibility of nearly degenerate adsorbate magnetic states. However, how these spins interact in real materials requires further theoretical study. We present results from Monte Carlo and Landau-Lifshitz-Gilbert equation simulations of spin systems relevant to superconducting qubits and resonators, as a function of applied field, temperature, and O_{2} coverage. The spin anisotropy and interactions in these models are parameterized with density functional theory calculations of specific defects. The phase diagram of the system, spin vortices, spin-spin correlations, and 1/w^{α} flux noise will be discussed, as well as the integration of these results into macroscopic qubit device models. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y33.00007: Collective effects based on direct dipole-dipole interaction in closely packed 3D transmon systems. Aleksei Sharafiev, Maximilian Zanner, Mathieu Juan, Phani Raja Muppalla, Gerhard Kirchmair Collective effects, including subradiance and superradiance, in many-body quantum systems were extensively studied theoretically since the seminal work of Dicke. Experimental studies in this area were initially performed in atomic physics experiments with a cavity mediated interaction between atoms. More recently similar experiments with two superconducting qubits have been performed using on-chip circuit QED architectures. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y33.00008: Photon-mediated Collective Effects Between Systems of Closely Packed 3D Transmons Maximilian Zanner, Aleksei Sharafiev, Gerhard Kirchmair Collective effects in many-body quantum systems were extensively studied theoretically and experimentally over the last decade. So far experiments were mainly relying on a single dominant coupling mechanism, either direct or photon-mediated. In this talk we present our experimental results with a system where both types of interaction are present and comparable in strength. We enter this regime with a 3D circuit QED platform, making use of the large, engineerable direct dipole-dipole interaction between qubits and a strong coupling to the fundamental mode of 3D rectangular waveguide. In particular we report on the collective dynamics of well separated pairs of closely packed 3D transmon qubits. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y33.00009: Interacting Qubit-Photon Bound States with Superconducting Circuits Neereja Sundaresan, Rex Lundgren, Guanyu Zhu, Alexey Gorshkov, Andrew Houck Strongly coupling a qubit to a photonic band-edge induces an exponentially localized photonic mode around the qubit, forming a qubit-photon dressed bound state [1]. Photonic crystals are a natural avenue to realize these bound states [2-3], and offer the ability to create one-dimensional chains of bound states with tunable and potentially long-range interactions that preserve the qubits' spatial organization. Here, we demonstrate tunable on-site and inter-bound state interactions in a two qubit microwave crystal. Interaction between bound states is set by photonic overlap, where localization changes with qubit detuning from the band-edge. This mechanism not only yields interaction strengths of 25-250 MHz between the lowest bound state transitions, but also a two-photon, virtual interaction as high as 15 MHz originating from a fourth order process in coupling. The widely tunable, high magnitude, robust interactions demonstrated with this system are promising benchmarks towards realizing new regimes with larger, more complex systems of bound states. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y33.00010: Interacting Qubit-Photon Bound States with Superconducting Circuits: Comparison of Theory and Experiment Rex Lundgren, Neereja Sundaresan, Guanyu Zhu, Alexey Gorshkov, Andrew Houck Qubits strongly coupled to a photonic crystal can give rise to many exotic physical scenarios, including the realization of certain quantum many-body models and single photon and multi-photon bound states which are localized around the qubits. Here, we consider two qubits connected to a superconducting, microwave photonic crystal. We demonstrate that this system allows for controllable interactions between the two qubits and observe a fourth-order two photon virtual process indicating strong coupling between the photonic crystal and qubits. In this talk, we focus on the theoretical modeling of this experimental system and compare experimental and theoretical results. By treating the photonic crystal as a one-dimensional hopping model, we find quantitative agreement with the experimental data, including two-photon results. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y33.00011: Fast storage and processing of qubit measurements Diego Riste, Brian Donovan, Guilhem Ribeill, Graham Rowlands, Daniel Ellard, Maika Takita, Markus Brink, Nicholas Bronn, Jay Gambetta, Jerry Chow The gate set of a logical qubit will include operations that are conditional on the measurement result of another logical qubit. For this result to be correctly interpreted, the computer must promptly determine the current Pauli frame, based on previous syndrome measurements. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y33.00012: Tunable coupling between long-lived microwave cavity modes Brian Lester, Yvonne Gao, Chen Wang, Serge Rosenblum, Luigi Frunzio, Michel Devoret, Steven Girvin, Liang Jiang, Robert Schoelkopf Superconducting microwave cavities are a promising resource for the storage of quantum states of photons. Further, coupling cavities to nonlinear transmon qubit modes enables the efficient manipulation and readout of these states. However, this results in increased relaxation and dephasing rates associated with the transmon. Thus, a direct coupling between neighboring cavities is a desirable resource for interfering quantum states stored in separate cavity modes. Here we discuss the implementation of an engineered coupling between two cavity modes via an RF-driven frequency-conversion that uses the nonlinearity of a transmon coupled to both cavities. Importantly, this coupling does not directly excite the transmon, thus suppressing the effect of transmon decoherence. We demonstrate the tunability of the coupling strength, which minimizes unwanted interactions, and realize a 50:50 beamsplitter two orders of magnitude faster than the cavity decoherence. We observe high-contrast interference between single microwave photons, which will be useful as an element in larger quantum algorithms. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y33.00013: Interference between microwave quantum memories Yvonne Gao, Brian Lester, Serge Rosenblum, Chen Wang, Luigi Frunzio, Michel Devoret, Liang Jiang, Steven Girvin, Robert Schoelkopf The ability to generate arbitrary quantum states on-demand, detect them with high fidelity, and excellent coherence properties of 3D cQED systems make them ideal platforms to solve boson sampling problems and implement linear-optics quantum computation (LOQC). In order to realise such protocols, we need robust beamsplitter and phase-shifting operations between cQED elements. Here, we use an RF-driven, frequency-converting beamsplitter between two superconducting memories to implement cascaded Mach-Zehnder interferometers. We use the dispersive coupling to perform phase control on the memory and demonstrate in-situ manipulation of the interference between two microwave photons at different frequencies. We show that this implementation is directly extended to multiphoton states and hence, can be applied to simulate complex high dimensional boson statistics. It is also compatible with qubits encoded in multi-photon states of cavities for quantum error correction, making such operations valuable for implementing logical gates between protected qubits. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y33.00014: Microwave Switches with Single Flux Quantum Control Zachary Keane, Ofer Naaman, Robert Hinkey, Alexander Marakov We present a superconducting microwave switch with multi-GHz bandwidth and single-flux-quantum (SFQ) control. We use the output of the switch to provide a highly energy-efficient method of communicating data from an SFQ logic circuit to room-temperature control hardware. The principle of operation, limitations, and use cases will be discussed. |
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