Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M37: Bosonic Qubits and CavitiesFocus Recordings Available
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Sponsoring Units: DQI Chair: Chiao-Hsuan Wang, University of Chicago Room: McCormick Place W-194B |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M37.00001: Waveguides with exceptional points of degeneracy for circuit QED Basil M Smitham, Christie S Chiu, Andrew A Houck The dispersion relation of a superconducting waveguide can be engineered by periodically modulating parameters along its length. Previous experiments have coupled superconducting qubits to the approximately quadratic band edges of microwave photonic crystals [1] [2]. However, higher-order polynomial dispersion is also possible, when multiple waveguides are side-coupled such that the resulting system has an exceptional point of degeneracy (EPD) [3]. EPDs of orders 3 (a cubic stationary inflection point), 4 (a quartic degenerate band edge), and higher have been realized with centimeter-scale copper waveguides [4]. In this talk I present experimental and theoretical progress towards realizing (greater than quadratic) exceptional points of degeneracy in a circuit QED architecture that consists of multiple superconducting coplanar waveguides periodically coupled in parallel. I also discuss how superconducting qubits can be coupled to these waveguides, with applications in slow light and multimode strong coupling. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M37.00002: Spontaneous emission dynamics of an artificial atom in the presence of non-perturbative light-matter coupling Kanupriya Sinha, Saeed A Khan, Elif Cuce, Hakan E Tureci Engineered superconducting electrodynamical systems provide a versatile platform for realizing some of the strongest interactions between light and matter, providing a glimpse of how basic notions anchored on perturbative quantum electrodynamics (QED) are modified in the presence of stronger light-matter interactions. A case in point are recent studies of high-impedance Josephson junction array (JJA) resonators which have been successfully put to use to study simulation of quantum impurity models. QED in such a setting requires a theoretical approach that intrinsically builds on non-perturbative coupling while still retaining the notion of modes that can be defined within a finite but open volume. We present one such approach that builds on what is known as the singular function expansion in the theory of integral equations, extending it to the quantum field theory domain. We show that the current experiments are in a regime where the notion of spontaneous emission is dramatically modified and propose an experiment to study the cross-over from a perturbative to non-perturbative regime |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M37.00003: Towards Fault Tolerant Joint Stabilizer Measurements for Bosonic Qubits: Part 1 Neel Thakur, James D Teoh, Benjamin J Chapman, Stijn de Graaf, Shruti Puri, Steven M Girvin, Luigi Frunzio, Robert J Schoelkopf Encoding qubits in the larger Hilbert space of cavity modes has many potential advantages due to superior coherence times and Bosonic error correction. However, to gain this benefit we must also be fault tolerant to errors in the non-linear element used for quantum control. Progress has been made in engineering fault tolerant single qubit measurements[1] and gates[2] for bosonic qubits. Ultimately, all operations, including two-qubit entangling operations, must be made similarly fault tolerant. We extend the scheme demonstrated in [1] to fault tolerant, QND joint photon number parity measurements by combining chi-matching and beamsplitter couplings between two cavities. These types of joint parity measurements are useful for Bell state generation, logical ZZ measurements and stabilizing concatenated codes for a variety of Bosonic encodings. In part 1 we describe the scheme and its fault tolerance properties. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M37.00004: Towards Fault Tolerant Joint Stabilizer Measurements for Bosonic Qubits: Part 2 James D Teoh, Neel Thakur, Benjamin J Chapman, Stijn de Graaf, Shruti Puri, Steven M Girvin, Luigi Frunzio, Robert J Schoelkopf Previously it was demonstrated that a fault tolerant parity measurement could be performed on Bosonic qubits[1]. In this scheme transmon ancilla errors do not propagate onto the logical qubit during the measurement. We extend this protocol to implement a fault tolerant joint-parity measurement on two logical qubits housed in cavities, serving as a measurement of the ZZ stabilizer. Our scheme requires only a switchable beamsplitter interaction between the cavities and an ancilla transmon coupled to just one of the cavities, reducing the need for complicated chi-matching requirements. We present preliminary experimental data demonstrating the protocol in a package containing two 3D stub cavities with beamsplitter couplings actuated by pumping a 3-wave-mixing element. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M37.00005: Tunable low-loss couplers integrated with superconducting 3d-cavities Ziyi Zhao, Eva Gurra, Eric I Rosenthal, Leila Vale, Gene C Hilton, Konrad Lehnert Superconducting circuits are a leading platform for quantum information processing. On one hand, the most coherent qubits are stored in (3-dimensional) microwave cavities; on the other hand, planar circuits provide design flexibility and large-scale manufacturability. A particularly desirable element would permit tunable, on-demand coupling of a 3d-cavity to a planar circuit, without introducing unwanted dissipation to the cavity. This element could be used, for example, to implement a modular quantum network, where any pairwise interactions between cavities could be turned on and off by connecting to a planar network. To this end, we design and test superconducting switches that tune the cavity external coupling from zero up to 3 orders of magnitude larger than the intrinsic cavity dissipation, while also preserving a 2.8 million cavity quality factor. Furthermore, the switches can be flipped in 10 ns, and remain in a linear regime at the microwave power needed for readout of a transmon qubit. |
Wednesday, March 16, 2022 9:00AM - 9:36AM |
M37.00006: Programmable operations between bosonic quantum elements Invited Speaker: Yvonne Y Gao The realisation of robust universal quantum computation with any platform ultimately requires both the coherent storage of quantum information and (at least) one entangling operation between individual elements. The use of multiphoton states encoded in superconducting microwave cavities as logical qubits is a promising route to preserve the coherence of quantum information against naturally-occurring errors. However, operations between such encoded qubits can be challenging due to the lack of intrinsic coupling between them. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M37.00007: Experimental realization of a stabilized pair coherent state in 3D cQED storage cavities. Shruti Shirol, Jeffrey Gertler, Chen Wang Preparing steady one-mode cat states in microwave cavities has led to applications like error-corrected bosonic logical qubits. A two-mode entangled state such as a pair coherent state│ξ, Δ〉= Σn C(ξ, n, Δ)│n+Δ, n〉, where ξ is a complex number, Δ is the photon number difference and coefficients C(ξ, n, Δ) have sub-Poissonian distribution, when used as a cat code for autonomous error correction promises significant advantages over one-mode cat-qubit. There is extensive theoretical research proposing the generation and stabilization of a pair coherent state from four-wave mixing and spontaneous emission that has not been realized experimentally yet. In this work, we prepare a stabilized pair coherent state in high-quality superconducting microwave storage cavities. The state is created from the vacuum and stabilized by engineering a two-photon exchange interaction of the cavities with the reservoir aid by four-wave mixing. In this talk, I will present our implementation of the dissipative process and show tomography results that prove the coherence in the prepared pair coherent state for long enough time before it decays into a classical mixture. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M37.00008: A 3-wave mixing beamsplitter between two bosonic modes Stijn de Graaf, Benjamin J Chapman, Jacob C Curtis, Yaxing Zhang, Nicholas E Frattini, Michel H Devoret, Steven M Girvin, Robert J Schoelkopf Quantum information processing using the bosonic modes of high-Q cavities aims to leverage long intrinsic lifetimes, while extending logical lifetimes by encoding information in the large Hilbert space provided and correcting for errors. In many bosonic encodings, a cavity-cavity beamsplitter interaction enables gates between multiple logical qubits. Gate performance using a transmon as a mixing element between cavities has been limited by unwanted Hamiltonian terms such as cross-Kerr arising from the transmon's 4th-order nonlinearity. A proposed solution is to use the 3rd-order nonlinearity of a SNAIL (Superconducting Nonlinear Asymmetric Inductive eLement) to mediate the interaction while suppressing unwanted 4th-order terms. We present an experimental implementation of a 3-wave mixing beamsplitter between high-Q cavities and benchmark its performance. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M37.00009: A controlled-SWAP operation between two bosonic modes Benjamin J Chapman, Stijn de Graaf, James D Teoh, Jacob C Curtis, Neel Thakur, Yaxing Zhang, Steven M Girvin, Michel H Devoret, Robert J Schoelkopf The coherence and large Hilbert spaces of three-dimensional superconducting microwave cavities make them an attractive platform for building quantum memories. Universal control of a single cavity mode can be accomplished by dispersively-coupling the cavity to a nonlinear mode such as a transmon. Wedding this resource with a bilinear cavity-cavity coupling such as a beamsplitter interaction provides a modular framework for quantum control of multiple cavities. Here we discuss a demonstration of this approach in the form of a Fredkin gate (controlled-SWAP) between a pair of cavities coupled by a three-wave mixing element, in which a transmon provides the control bit for the SWAP. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M37.00010: Advancements in 3D cavity fabrication for improved quantum memories Andrew Oriani, Srivatsan Chakram, David Schuster, Kevin He, Ankur Agrawal, Tanay Roy High coherence 3D cavities have allowed for the creation of single and multimode quantum memories and the creation of non-trivial bosonic states that can be stabilized against decay. Scaling the number of accessible modes in these systems will require the creation of cavities with very long coherence times. In this talk we will discuss the creation of ~6.5GHz niobium coaxial cavities with single-photon internal quality factors in excess of 1.4 billion with conduction-limited quality factors greater than 3 billion. This will include a discussion of the surface processing and a characterization of the intrinsic loss mechanisms and methods for reducing these losses. Finally, we will discuss the challenges of qubit integration and the creation of single and multimodal quantum memories using such long-lived cavity states. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M37.00011: Characterization of magnetic levitation within a microwave cavity Nabin K Raut, Jeffery Miller, Raymond Y Chiao, Jay E Sharping A mechanical coupling within a microwave cavity shows rich physics from the test of fundamental physics to semi-classical to quantum to novel physics. Such coupling to the levitated mechanical oscillator is promising for reducing losses that come about from clamping and reduced thermal contact. We experimentally, theoretically, and analytically characterized Meissner-effect levitation within a 10 GHz superconducting aluminum coaxial quarter-wave stub cavity for a sequence of identically shaped millimeter-scale neodymium magnets having varying strengths (1.22-1.47 T). In the microwave spectra collected from 5 K (well above the transition temperature of aluminum) to 50 mK (base temperature of the dilution refrigerator), we observed shifts in the spectra corresponding with the change in the total quality factor of the cavity. A large change in the resonance frequency with height, exhibiting a sensitivity as large as 400 MHz/mm and a sharp rise in the quality factor of 8%-17%, is observed during magnetic levitation. There is an excellent agreement between our experimental measurements and the expected results from a circuit model for the system. Prior to magnet motion and levitation, the Q of the cavity changes quadratically with temperature, as expected, as the walls of the cavity undergo the superconducting transition. We observe, however, a deviation from the quadratic trend as a function of temperature which is attributable to magnet movement within the cavity. |
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