Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q37: 3D and MultiMode Cavity DevicesFocus Recordings Available

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Sponsoring Units: DQI Chair: Srivatsan Chakram, Rutgers University Room: McCormick Place W194B 
Wednesday, March 16, 2022 3:00PM  3:12PM 
Q37.00001: A novel package for fastflux delivery in 3D Yao Lu, Aniket Maiti, Suhas S Ganjam, John W Garmon, Yaxing Zhang, Steven M Girvin, Luigi Frunzio, Robert J Schoelkopf Parametric flux modulation of SQUIDs and other fluxtunable devices has shown great promise in engineering fast gate operations and nonlinear quantum interactions. However, its applications have been primarily limited to 2D planar architectures. The efficient delivery of fast flux modulation in 3D architectures, potentially allowing the integration of fast parametric interactions with highly coherent 3D quantum memories, has been a tempting yet challenging task. Here we propose a novel design that allows such an efficient delivery of dc and ac flux into a 3D superconducting package without driving the charge degree of freedom, while preserving the coherence properties of the device. As an example, we show how our design enables the parametric modulation of a dc SQUID device, and demonstrate how highfidelity operations can be achieved. 
Wednesday, March 16, 2022 3:12PM  3:24PM 
Q37.00002: A frequencymodulated beamsplitter between 3D quantum memories Aniket Maiti, Yao Lu, Suhas S Ganjam, John W Garmon, Yaxing Zhang, Steven M Girvin, Luigi Frunzio, Robert J Schoelkopf Achieving fast, tunable, highfidelity bilinear interactions between 3D bosonic memories is a compelling goal in circuitQED. To facilitate this, these memories are often coupled to a nonlinear element that activates specific interactions dependent on the frequency of drive tones applied to it. Strong drives usually result in faster interactions, but a linear coupling to the drive results in a displacement of the nonlinear mode and triggers other undesirable processes, reducing the fidelity of the operation. To mitigate this, we use a symmetric DC squid with the common mode acting as the nonlinear mode used in the interaction, and the differential mode being pumped to turn the interaction on and off. This effectively gives us a frequency modulation of the common mode without displacing it. We are able to selectively pump the differential mode through a carefully engineered AC flux drive, achieving a parametrically driven highfidelity beamsplitting process. 
Wednesday, March 16, 2022 3:24PM  3:36PM 
Q37.00003: Characterization of lefthanded metamaterial ring resonator coupled to transmon qubits Jaseung Ku, Tianna A McBroom, Bradley G Cole, Britton L Plourde Lefthanded metamaterial transmission line resonators made from an array of superconducting lumped elements possess unique dispersion relations. Unlike conventional righthanded transmission line resonators, they can exhibit a high density of modes in a frequency range of less than one GHz, which allows for the coupling of superconducting qubits to multiple modes. A lefthanded transmissionline ring resonator can support dense mode spectra in a compact footprint, which holds promise for quantum memories and compact quantum processing nodes of a distributed quantum network. We have fabricated lefthanded metamaterial ring resonators that are directly coupled to multiple transmon qubits at different locations around the ring. In this talk, we will present the experimental measurements on such a lefthanded metamaterial ring resonator, including the characterization of the mode spectra and the coupling to multiple transmon qubits. 
Wednesday, March 16, 2022 3:36PM  3:48PM 
Q37.00004: Manybody states of radiation in a FabryPerot cavity coupled to a single qubit Nitish Mehta, Roman Kuzmin, Cristiano Ciuti, Vladimir Manucharyan We explore a new regime of quantum electrodynamics achieved when a strongly anharmonic qubit is coupled to a FabryPerot resonator with a strength greater than the free spectral range. The qubit mediates a coherent hybridization of singlephoton excitations with a class of manybody states of radiation, involving several photons in the low frequency modes. We experimentally realize this new regime by galvanically coupling a fluxonium qubit to a long section of 1D transmission line resonator and performing linear microwave spectroscopy. As a result, the nearly equidistant FabryPerot spectrum acquires a rich fine structure. This effect was missed in the previous theoretical studies of the superstrong coupling regime, and it is strongly suppressed for a weakly anharmonic qubit, such as transmon. We propose an effective description for the manybody spectrum which matches hundreds of energy levels without adjustable parameters. 
Wednesday, March 16, 2022 3:48PM  4:00PM 
Q37.00005: Numerical Gate Synthesis for Quantum Heuristics on MultiMode Bosonic Systems A. Baris Ozguler, Davide Venturelli There is a recent surge of interest and insights regarding the interplay of quantum optimal control and variational quantum algorithms [1]. We study the framework in the context of qudits which are, for instance, definable as controllable electromagnetic modes of a superconducting cavity system coupled to a transmon. By employing the quantum optimal control approaches described in [2,3], we showcase universal control of singlequdit operations up to 8 states, and twoqutrit operations, mapped respectively on a single mode and two modes of the resonator. We discuss the results of numerical pulse engineering on the closed system for parametrized gates useful to implement QAOA qudit algorithms [4]. The results show that high fidelity (> 0.99) is achievable with sufficient computational effort on HPC for all cases under study, and extension to multiple modes and open, noisy systems are possible. The tailored pulses can be stored and used as calibrated primitives for a future compiler in cQED systems. 
Wednesday, March 16, 2022 4:00PM  4:36PM 
Q37.00006: Investigate material losses in superconducting circuits with multimode resonators. Invited Speaker: Chan U Lei High Q superconducting cavities are important resources in superconducting quantum circuits. The longlived bosonic modes in the cavities can be used to store quantum information and enable quantum error correction in a hardwareefficient manner. Improving the coherence of superconducting cavities is crucial to realize practical quantum processors with 3D circuit QED architecture. The coherence of superconducting circuits and superconducting cavities is limited by the losses from their constituent materials. Quantifying the material losses in the devices is crucial to understanding the loss mechanism and improving coherence. In this work, we present a method to quantify material losses using multimode superconducting resonators. We apply this technique to measure the material loss properties of aluminum, including the surface resistance, seam conductance, and loss tangent of the surface oxide. Additionally, we use this technique to study the chemical etching process and quantify the improvement on the material losses. The extracted material losses are valuable information to optimize the circuit designs and fabrication processes. More importantly, correlating the losses with material properties acquired from other material characterization techniques could provide significant insight into the underlying loss mechanism, which is crucial for substantial improvements in material qualities and coherence. 
Wednesday, March 16, 2022 4:36PM  4:48PM 
Q37.00007: Robust preparation of Wignernegative states with optimized SNAPdisplacement sequences Marina Kudra, Mikael Kervinen, Ingrid Strandberg, Shahnawaz Ahmed, Marco Scigliuzzo, Amr Osman, Daniel Perez Lozano, Anton Frisk Kockum, Isaac Quijandria Diaz, Per Delsing, Simone Gasparinetti Hosting nonclassical states of light in 3D microwave cavities has emerged as a promising paradigm for continuousvariable quantum information processing. Here we experimentally demonstrate highfidelity generation of a range of Wignernegative states useful for quantum computation, such as Schrödinger cat states, binomial states, GottesmanKitaevPreskill (GKP) states and cubic phase states. To do so, we use a sequence of interleaved selective numberdependent arbitrary phase (SNAP) gates and displacements. We use two steps of optimization. In the first step we use a gradient descent algorithm to optimize the parameters of the SNAP and displacement gates. In the second step we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly nonclassical states in a harmonic oscillator is robust to fluctuations of system parameters such as the qubit frequency. 
Wednesday, March 16, 2022 4:48PM  5:00PM 
Q37.00008: Circuit QED implementation of the nonperturbative boundary sineGordon model. Sebastien Leger, Theo Sepulcre, Cecile Naud, Olivier Buisson, Wiebke Hasch, Izak Snyman, Denis Basko, Serge Florens, Nicolas Roch Quantum impurity problems, that describe the interaction between a degree of freedom (DOF) and an environment, are at the heart of a very rich physics covering fields as diverse as quantum optics and strongly correlated matter. In this work, we use the tools of circuit QED to address a quantum impurity problem called Boundary Sine Gordon (BSG). 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q37.00009: Stabilization of multimode Schrodinger cat states via normalmode dissipation engineering Petr Zapletal, Andreas Nunnenkamp, Matteo Brunelli NonGaussian quantum states have been autonomously stabilized in single and twomode circuit QED architectures via engineered dissipation. Here, we upgrade dissipation engineering to collective modes of resonator arrays and show how to stabilize multimode Schrodinger cat states, delocalized over an arbitrary number of cavities. We consider tailored dissipative coupling between resonators that are parametrically driven and feature an onsite nonlinearity, which is either a Kerrtype nonlinearity or an engineered twophoton loss. We find exact closedform solutions for the twodimensional steadystate manifold spanned by multimode cat states. We further show that, in the Zeno limit of strong dissipative coupling, multimode cat states can be deterministically prepared. Remarkably, engineered twophoton loss gives rise to a fast relaxation towards the steady state, protecting the state preparation against decoherence due to intrinsic singlephoton losses and imperfections in tailored dissipative coupling. The relaxation time is independent of system size making the state preparation scalable. Multimode cat states are naturally endowed with a noise bias that increases exponentially with system size and can thus be exploited for enhanced robust encoding of quantum information. 
Wednesday, March 16, 2022 5:12PM  5:24PM 
Q37.00010: A ringresonator based coupler with tunability for ondemand connectivity in a superconducting multiqubit network Anirban Bhattacharjee, Sumeru Hazra, Jay Deshmukh, Meghan P Patankar, Rajamani Vijayaraghavan Recently, we demonstrated a ringresonator based architecture in 3D cQED [1] for enhanced connectivity in a superconducting multiqubit network without compromising coupling uniformity. This design can be extended to build highly connected processors using large number of qubits. However, building processors with alwayson interqubit coupling can lead to coherent errors due to several connected spectator qubits. Introducing tunable couplers can enable activation of coupling on demand between a subset of qubits within a larger network. This reduces unwanted crosstalk and offers flexibility for different applications. 
Wednesday, March 16, 2022 5:24PM  5:36PM 
Q37.00011: Optimising multiqubit operations in a ringresonatorbased quantum processor Sumeru Hazra, Gautham Umasankar, Aakash V, Kaushik Singirikonda, Jay Deshmukh, Sai Vinjanampathy, Rajamani Vijayaraghavan A highly connected qubit network enables one to efficiently compile an arbitrary quantum operation by minimizing gate count. Recently, we showed that a highly connected superconducting qubit network could be achieved using a ringresonatorbased coupler [1]. However, in architectures with static coupling, many levels (including noncomputational ones) in the extended Hilbert space may interact with each other and cause undesired shifts in the computational subspace, leading to coherent errors. Using the ringresonatorbased coupler architecture, we explore the optimization of device parameters for a given number of transmon qubits and connectivity, to achieve maximum processor performance. We also investigate the possibility of using optimalcontroltechniques[2] that include the coherent errors in the system Hamiltonian to tune highfidelity quantum operations in such connected networks consisting of five to ten qubits. 
Wednesday, March 16, 2022 5:36PM  5:48PM 
Q37.00012: Ultracompact cavity array for analog quantum simulation Vincent Jouanny, Vera Jo Weibel, Fabian Oppliger, Simone Frasca, Edoardo Charbon, Pasquale Scarlino Photonic cavity arrays form the basis of one of the most promising paradigms for quantum simulation to study complex manybody physics. We developed a nontrivial structured photonic environment that could enable a multimode strong and ultrastrong coupling with a qubit. This platform consists of a unidimensional metamaterial implemented by an array of coupled superconducting microwave cavities made from thin Niobium Nitride (NbN) films. Such disordered superconductor allows to reach a very high kinetic inductance, which presents a twofold advantage: a) It allows to reach ultrastrong coupling with an artificial atom as the capacitive coupling is proportional to the square root of the resonators' impedance, which can be highly increased thanks to the kinetic inductance; b) It allows to strongly reduce the resonator/metamaterial footprint. Furthermore, working with a metamaterial allows the engineering of a nontrivial photonic dispersion relation, where it is possible to obtain states displaying topological properties (SSHstates). We have been able to fabricate and characterize unidimensional metamaterials made of up to 88 ultracompact resonators. We are currently expanding this technology to 2D metamaterials, where we expect to engineer further topological photonic states. 
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