Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W67: Continuous-Variable Quantum Information: HardwareFocus
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Sponsoring Units: DQI Chair: Yuxin Wang, University of Chicago Room: Room 412 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W67.00001: Scalable and Programmable Phononic Network Using Vibrational Modes of Trapped Ions Invited Speaker: Kihwan Kim Trapped ion system is one of the leading physical platforms to realize a practical quantum computer and quantum simulator. Recently, the vibrational degrees of freedom of trapped ions have been extensively studied and are getting attentions for the application to quantum information processing with continuous variables [1]. In particular, phonons in multiple vibrational modes can be configured as bosonic networks that can perform boson sampling to reveal quantum advantage. Differently from photonic systems the phonon number states in the phononic systems can be deterministically prepared and detected and the total number of phonons is well conserved for all the collective modes except the center of mass mode. However, to our knowledge, there has been no experimental realization of a phononic network with more than two modes. Here we present the phononic network that consists of up to four modes with the capability of programming an arbitrary network as well as the deterministic preparation and detection. In the network, beam splitting operations between any pairs of modes are implemented through the coupling with ion-qubits [2]. As the benchmark of the performance of the phononic network, we demonstrated the algorithms of tomography for any multi-modes phononic states in a single measurement configuration [3]. Our experiment demonstrates a clear and novel pathway to scale up a phononic network for various quantum information processing beyond the limitations of classical and other quantum systems. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W67.00002: Fast coherent swaps between high-Q bosonic modes with a parity-protected coupler Aniket Maiti, Yao Lu, John W Garmon, Suhas S Ganjam, Yaxing Zhang, Jahan Claes, Luigi Frunzio, Robert J Schoelkopf Superconducting resonators with long lifetimes and a highly biased noise channel have shown promise for CVQC in the last decade, with demonstrations of universal single-mode control and error correction beyond break-even. For scaling up this architecture, fast, clean, and tunable multi-cavity operations that do not spoil their lifetime and noise bias are highly desirable. In the past, this has been difficult because the source of non-linearity that enables such operations also introduces spurious processes that lead to heating and dephasing, limiting the operation's fidelity. We show that applying a selectively differential pump to a DC-SQUID gives us a coupling mechanism that is parity-protected, only allowing processes that couple an even number of pump photons to an even number of mode quanta. This circumvents the previously mentioned difficulties, letting us implement a highly coherent beamsplitter between two cavities limited only by their single-photon loss. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W67.00003: Characterizing Control of a High Fidelity Beamsplitter in the Single-Photon Subspace John W Garmon, Yao Lu, Aniket Maiti, Suhas S Ganjam, Yaxing Zhang, Jahan Claes, Luigi Frunzio, Robert J Schoelkopf Recent demonstrations of highly coherent beamsplitting interactions between two high-Q bosonic modes in circuit QED platforms motivate us to characterize our control of this interaction under pulsed operation. To do this, we work in the joint single photon subspace of the two-cavity system ({|01>, |10>}), which can be mapped onto a Bloch Sphere. Here, the beamsplitter interaction generates arbitrary rotations, allowing us to apply conventional qubit control characterization techniques to this system. After tuning up beamsplitter gates in the presence of drive-induced frequency shifts, we run a randomized benchmarking protocol, achieving an average gate fidelity of F > 99.90%. Further, we show that the fidelity is mostly limited by cavity decay, which suggests an ultimate fidelity approaching 99.99% should be possible. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W67.00004: Universal control of a bosonic mode in a planar superconducting nonlinear resonator via native interactions Axel M Eriksson, Théo Sépulcre, Mikael Kervinen, Timo Hillmann, Marina Kudra, Dupouy Simon, Yong Lu, Maryam Khanahmadi, Jiaying Yang, Claudia Castillo Moreno, Per Delsing, Simone Gasparinetti Bosonic modes, thanks to their large Hilbert space, offer a hardware-efficient alternative for quantum information processing. However, to operate linear bosonic modes, some nonlinearity is still required, which is typically realized by an ancilla qubit. We present a bosonic mode consisting of a superconducting nonlinear asymmetric inductive element (SNAIL)-terminated planar resonator, which is not controlled by an ancilla qubit but via the nonlinearities in the SNAIL element. The Kerr nonlinearity is canceled by tuning the flux through the SNAIL to realize a close to linear mode when the system is idling. The off-resonant strong third order nonlinearity can be activated by applying a flux pulse at three times the frequency of the bosonic mode. Hence, the resulting tri-squeezing interaction promotes the more easily accessible Gaussian interactions to a universal gate set. By combining these interactions, we experimentally demonstrate Wigner-negative states such as the cubic phase state. Furthermore, the operation of these native squeezing and tri-squeezing interactions can be combined with standard ancilla qubit control and thereby boost the control capabilities. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W67.00005: Fast entanglement of weakly interacting harmonic oscillators with superconducting qubits for bosonic encoded quantum computation Asaf A Diringer, Eliya Blumenthal, Shay Hacohen-Gourgy Bosonic encoding is a relatively nascent path to quantum computation in circuit QED. Dispersively coupling multiple Bosonic modes to a single superconducting ancilla qubit can be used to create entanglement between the bosonic modes. Typically these schemes use a large coupling of the bosonic modes to the ancilla for fast operation, however, this creates undesired anharmonicity in the form of Kerr nonlinearities, which degrade performance. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W67.00006: Fast Control of Multimode Cavities with Conditional Displacements Eesh A Gupta, Thomas J DiNapoli, Jordan Huang, Ming Yuan, Kevin He, Liang Jiang, David Schuster, Srivatsan Chakram One promising implementation of quantum computers is a high-Q 3D multimode cavity coupled to superconducting transmon circuits. A key limitation of this architecture are the ancillary transmons, which limit the fidelity of gate operations and lower cavity coherence via the inverse Purcell effect. In order to mitigate these errors, a recently proposed pulse scheme uses large oscillator displacements to achieve an effective conditional displacement interaction [1]. Such a displacement acts as a “switch” to temporarily turn on the oscillator’s interaction strength with the qubit. In doing so, this technique maintains gate speeds while mitigating ancilla errors by weakening the bare dispersive interaction. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W67.00007: Coherence Preserving Tunable Coupler For 3D Cavities Nicholas Materise, Srivatsan Chakram, Jens Koch, Eliot Kapit Superconducting 3D cavities remain the highest coherence objects in the circuit QED community. Control of these long lifetime cavity states requires a nonlinear element, typically a transmon circuit with dipole coupling to one or many cavity modes. Charge drives applied to these transmons have used to demonstrate both beam-splitter and two mode squeezing interactions between neighboring cavities via four wave mixing, but Purcell loss and dielectric loss from the transmon substrate limit the performance of these couplers. We propose a tunable coupler that preserves the coherence of the neighboring cavities by minimizing interactions with lossy degrees of freedom while maintaining a high on/off ratio in coupling strengths. We present a practical tunable coupler implementation using existing high-Q 3D cavity fabrication techniques and estimate the performance of parametric operations between two cavities connected to the coupler. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W67.00008: A hybrid controlled-SWAP gate between two bosonic modes Sophia H Xue, Stijn J de Graaf, Benjamin J Chapman, Yaxing Zhang, James D Teoh, Jacob C Curtis, Takahiro Tsunoda, Alec W Eickbusch, Alexander P Read, Akshay Koottandavida, Shantanu O Mundhada, Luigi Frunzio, Michel H Devoret, Steven M Girvin, Robert J Schoelkopf The controlled-SWAP (cSWAP) gate, which exchanges the states of two qubits conditioned on the state of an ancilla qubit, is at the heart of the SWAP-test sequence for quantum state comparison, as well as proposals for quantum random access memory. We implement this gate in an architecture that combines a tunable beamsplitter interaction between two bosonic modes in superconducting microwave cavities with universal single cavity control provided by a dispersively coupled transmon ancilla. Until now, the fidelity of cSWAP has been limited by transmon errors during the long SWAP time (~10us). By using a purpose-built SNAIL coupler to mediate cavity-cavity interaction, we achieve a 10x faster beamsplitter rate (on the order of the dispersive shift) while preserving cavity coherence, thereby reducing the cSWAP gate time to 1.3us. We then show how this tool can be used to generate entanglement by preparing a Bell state with measurement-corrected fidelity of 95%. Finally, we show how SWAP tests can be used to purify a quantum state from two imperfect copies. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W67.00009: Tunable coupling between superconducting 3d cavities via integrated low-loss couplers on a planar circuit Ziyi Zhao, Eva Gurra, Leila Vale, Michael R Vissers, Konrad Lehnert Modular quantum networks consisting of superconducting circuits are a promising approach to processing large scale quantum information tasks. To utilize the high quality factor 3-dimensional microwave cavities as the memory component within the modules, an ongoing challenge is to implement rapid, reconfigurable, and low-loss swap interactions among the cavities. One approach is to interface the cavities with a planar circuit to mediate the interaction, on which the switching elements can be tuned to change the coupling strength. This leverages the design flexibility and large-scale manufacturability of planar circuits to allow for more suitable and better performing switching elements. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W67.00010: Efficient simulations of Lindblad master equations in the stabilized code space of cat qubits François-Marie Le Régent, Jérémie Guillaud, Pierre Rouchon We introduce a new method to obtain effective reduced dynamics on the decoherence-free subspace of a dissipative Lindblad dynamics having multiple degenerate steady states. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W67.00011: Coherent cancellation of tunneling and quantum information protection: the Delta variant of the Kerr-cat qubit - Part 1/3 Rodrigo G Cortinas, Jayameenakshi Venkatraman, Nicholas E Frattini, Xu Xiao, Michel H Devoret Encoding and manipulating quantum information with logical cat qubits is a promising means to perform quantum error correction, but controlling undesired parametric processes, while preserving quantum control, remains an outstanding challenge. The Kerr-cat qubit, created by squeeze-driving a weakly nonlinear Kerr oscillator, provides a double-well system with minimal spurious parametric processes. The tunnel effect is expected to be cancelled in its ground state manifold. The logical errors induced by incoherent well-flipping are then dominated by tunneling through excited states under incoherent excitations. A key question is, how does this incoherent well-flipping affect the qubit manifold? Moreover, can the cancellation of tunneling be extended to the higher excited states? |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W67.00012: Coherent cancellation of tunneling and quantum information protection: the Delta variant of the Kerr-cat qubit - Part 2/3 Jayameenakshi Venkatraman, Rodrigo G Cortinas, Nicholas E Frattini, Xu Xiao, Michel H Devoret Encoding and manipulating quantum information with logical cat qubits is a promising means to perform quantum error correction, but controlling undesired parametric processes, while preserving quantum control, remains an outstanding challenge. The Kerr-cat qubit, created by squeeze-driving a weakly nonlinear Kerr oscillator, provides a double-well system with minimal spurious parametric processes. The tunnel effect is expected to be cancelled in its ground state manifold. The logical errors induced by incoherent well-flipping are then dominated by tunneling through excited states under incoherent excitations. A key question is, how does this incoherent well-flipping affect the qubit manifold? Moreover, can the cancellation of tunneling be extended to the higher excited states? |
Thursday, March 9, 2023 5:48PM - 6:00PM |
W67.00013: Modeling coherent-state lifetime in Kerr-cat qubits - Part 3/3 Qile Su, Rodrigo G Cortinas, Jayameenakshi Venkatraman, Michel H Devoret, Shruti Puri The Kerr-cat qubit is encoded in even and odd superpositions of coherent states and is realized by applying a squeezing drive to a Kerr nonlinear oscillator. The possibility to extend the coherent-state lifetime by increasing the squeezing amplitude makes the Kerr-cat qubit an attractive realization of a biased-noise qubit. Experiment shows that this lifetime indeed increases as a function of squeezing amplitude, but only does so abruptly whenever a new pair of the Kerr-cat's energy levels become quasi-degenerate. How can theory explain the surprising connection between the energy levels and the coherent-state lifetime? Assuming single-photon loss and gain, we observe that one eigenvalue of the Lindbladian super-operator largely determines the coherent-state lifetime. By calculating this eigenvalue perturbatively, we show that the lifetime is limited by leakage into levels outside the Kerr-cat qubit's double-well potential. Whenever a pair of levels fall into the double well and become quasi-degenerate, leakage out of the double well is reduced, leading to an abrupt increase in the coherent-state lifetime. Our Lindbladian approach complements direct master equation simulations and additionally identifies the important eigenstates of the system. |
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