Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D08: Quantum Control and Quantum Gates |
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Sponsoring Units: DQI Chair: Gregory Quiroz, Johns Hopkins University Room: 104 |
Monday, March 2, 2020 2:30PM - 2:42PM |
D08.00001: Simulated Randomized Benchmarking of Dynamically Corrected Cross-Resonance Gate Ralph Kenneth Colmenar, Jason Paul Kestner We theoretically simulate a cross-resonance (CR) gate implemented by pulse sequences proposed in Phys.Rev. Lett. 118, 150502 (2017). These sequences allow mitigation of systematic noise to first order, but their effectiveness is limited by one-qubit gate imperfections. To improve the feasibility of such sequences, we make use of the fact that arbitrary Z rotations can be implemented virtually and with negligible error. We illustrate this by simulating randomized benchmarking for a system of coupled transmons and show that it is possible, under certain conditions, to improve the CR gate fidelity in the presence of quasistatic noise. |
Monday, March 2, 2020 2:42PM - 2:54PM |
D08.00002: Experimental protection of qubit coherence up to relaxation times by using an image drive Sylvain Bertaina, Herve Vezin, Irinel Chiorescu The protection of spin coherence is an essential task in order to manipulate, store and read quantum information. It has been proposed to dynamically decouple (DD) qubits from their surroundings by applying a series of distinct pulses^{1}. For nitrogen vacancy centers, such protection was achieved by using concatenated DD up to the second order of dressing^{2,3}. We go beyond their specific case and demonstrate a new pulse protocol in a number of materials with different spin Hamiltonians and environments. We demonstrate the regime T2~T1 for temperatures ~40K. The protocol uses two coherent microwave pulses: one drives the Rabi precession while a low-power, circularly polarized (image) pulse continuously sustains the spin motion. The initial phase of the image drive allows tuning the spin dynamics by altering the Floquet modes. The technical implementation is simple and can be generalized to any type of qubit, such as superconducting circuits or spin systems. |
Monday, March 2, 2020 2:54PM - 3:06PM |
D08.00003: Complete quantum-state tomography with a local random field Christian Arenz, Ralf Betzholz, Jianming Cai Single-qubit measurements are typically insufficient for inferring arbitrary quantum states of a multi-qubit system. We show that if the system can be fully controlled by driving a single qubit, then utilizing a local random pulse is almost always sufficient for complete quantum-state tomography. Experimental demonstrations of this principle are presented using a nitrogen-vacancy (NV) center in diamond coupled to a nuclear spin, which is not directly accessible. We report the reconstruction of a highly entangled state between the electron and nuclear spin with fidelity above 95%, by randomly driving and measuring the NV-center electron spin only. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D08.00004: High sensitivity spectral characterization of local microwave fields using two-photon absorption processes of a transmon qudit Spencer Tomarken, Jonathan L DuBois Optimal control methods for quantum information processing require precise knowledge of the local microwave amplitudes generated by control pulses arriving at the cryogenic stage of the quantum processor. We present a scheme for characterizing the spectral transfer function of a superconducting transmon qudit capacitively coupled to a 3D cavity resonator. We apply two simultaneous drive tones close to the transmon's 0-1 and 1-2 state transition frequencies while varying both the duration of the pulses as well as their relative detuning. Through measurement of the 0-, 1-, and 2-state occupations, we map out the 0 to 2 state two-photon absorption process.The relative occupation of the three lowest transmon levels provides a sensitive probe of the local microwave field over a large range of detuning. By comparing our measurement results to master equation simulations incorporating a spectral filter, we recover the amplitude-corrected transfer function over an approximately 200 MHz bandwidth. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D08.00005: Implementation of the XY interaction family by calibration of a single pulse Deanna Abrams, Nicolas Didier, Blake Johnson, Marcus P Da Silva, Colm Ryan Near-term applications of quantum information processors will rely on optimized circuit implementations to minimize gate depth and therefore mitigate the impact of errors in noisy intermediate-scale quantum (NISQ) computers. More expressive gate sets can significantly reduce the gate depth of generic circuits. Similarly, structured algorithms can benefit from a gate set that more directly matches the symmetries of the problem. The XY interaction generates a family of gates that provides expressiveness well tailored to quantum chemistry as well as to combinatorial optimization problems; while also offering reductions in circuit depth for more generic circuits. Here we implement the full family of XY entangling gates in a transmon-based superconducting qubit architecture using a composite pulse scheme that requires calibration of only a single gate and maintains constant gate time for all members of the family. This allows us to maintain a high fidelity implementation of the gate across all entangling angles. The average fidelity of gates sampled from this family ranges from 95.67 ± 0.60% to 99.01 ± 0.15%, with a median fidelity of 97.35 ± 0.17%, which approaches the coherence-limited gate fidelity of the qubit pair. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D08.00006: Selective number-dependent arbitrary Hamiltonian engineering for a cavity Chiao-Hsuan Wang, José Lebreuilly, Kyungjoo Noh, Steven Girvin, Liang Jiang Cavity resonators are promising resources for storing and processing quantum information. Here we investigate a scheme to engineer the Hamiltonian for a photonic cavity using an ancilla qubit. In the strong dispersive coupling limit and number-split regime, one can drive the qubit near selective photon-number-dependent transition frequencies to address the individual photon number states of the cavity. By choosing control driving detunings much larger than the driving strengths, we propose a general approach to engineering a selective number-dependent arbitrary Hamiltonian for the cavity. The engineered Hamiltonian admits various applications including canceling unwanted cavity Kerr effect, creating higher-order nonlinearities for quantum simulations, designing quantum gate operations resilient to noise, and even realizing quantum error correction. Our scheme can be implemented with a coupled microwave cavity and transmon qubit in superconducting circuits systems. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D08.00007: Implementing robust Holonomic quantum gates using dynamical invariant Yingcheng Li, Yidun Wan Holonomic quantum computing operates quantum systems using berry's phase, or more generally, Aharanov-Anandan phase. It is proved that quantum gates implemented by using these geometric phases are more robust against certain errors. While Holonomic gates have been realized in many systems, extra degrees of freedom are usually required. In this work, we propose a general dynamical invariant for 1 qubit and 2 qubit that is restricted in logical space that enables holonomic quantum computing without inverse engineering. In particular, a Holonomic CNOT gate can be implemented with extremely high fidelity. Moreover, an investigation in the aspect of geometry shows the Hamiltonians used to control the system all have monopole-type gauge field in parameter space, which provides a hidden mathematical structure that contributes to extra robustness. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D08.00008: Superconducting cavity QED: box modes for quantum control of qubits Raina Olsen, Mohammadreza Rezaee, Eliahu Cohen, Ebrahim Karimi Circuit QED uses two types of superconducting cavities: one-dimensional superconducting resonators that contain charge excitations, and two or three-dimensional regions of space between superconducting mirrors that contain photons. This latter type of cavity does not necessarily need to be enclosed. Any superconducting circuit acts as a cavity for the surrounding photonic modes with wavelengths on the order of the circuit geometry. Normally these are referred to as box modes, and treated primarily as a source of dissipation (except when a box mode frequency happens to be close to qubit frequencies). However, quantum transduction methods show that a system can be designed so that energy flows between modes at very different frequencies. We treat the problem of a superconducting qubit in a THz cavity by quantizing Maxwell’s equations, showing that the driven system is described by the linearized Hamiltonian of cavity optomechanical systems used for quantum transduction. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D08.00009: Adiabatic Quantum Control of Dissipative State Preparation Emery Doucet, Tristan Brown, Archana Kamal Dissipative protocols for state preparation provide the ability to produce complex entangled states which are inherently robust to decoherence. Protocols based on parametric interactions are particularly powerful in this regard, with the potential for much superior performance compared to resonant schemes while simultaneously providing a large degree of flexibility and control over the stabilized state [1]. In this talk I will describe a scheme for preparing Bell states which employs only parametric qubit-qubit and qubit-resonator couplings. Both the amplitudes and phases of these couplings are tunable in situ, providing a natural avenue to implement time-dependent control of the state preparation dynamics. I will present numerical and analytical results on the application of time-dependent parametric controls while ensuring that the evolution is adiabatic, such that the system remains in the instantaneous dark state of the dynamics. Such fast time-dependent control is within reach of current experimental capabilities, and can enable a large (>10x) reduction in state preparation times. [1] E. Doucet, F. Reiter, L. Ranzani, and A. Kamal, arXiv:1810.03631 (2018). |
Monday, March 2, 2020 4:18PM - 4:30PM |
D08.00010: Investigating the speed limit of two-qubit entangling gates with superconducting qubits Joel Howard, Junling Long, Mustafa Bal, Ruichen Zhao, Tongyu Zhao, David Pappas, Zhexuan Gong, Meenakshi Singh Fast two-qubit entangling gates are essential for quantum computers with finite coherence times. Due to the limit of interaction strength among qubits, there exists a theoretical speed limit for a given two-qubit entangling gate. This speed limit has been explicitly found only for a two-qubit system and under the assumption of negligible single qubit gate time. We demonstrate such speed limit experimentally using two superconducting transmon qubits with an always-on capacitive coupling. Moreover, we investigate a modified speed limit when single qubit gate time is not negligible, as in any practical experimental setup. Finally, we discuss the generalization to multiple qubit systems where the coupling to additional qubits can significantly increase the speed limit of a two-qubit entangling gate, thus requiring the co-design of the quantum computer from both theorists and experimentalists for optimal gate performance. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D08.00011: High fidelity quantum gates for NV center defect registers based on dynamical decoupling sequences Wenzheng Dong, Fernando A Calderon, Sophia Economou The spinful nuclei surrounding a defect such as the NV center in diamond are promising qubits for a modest-size quantum register. Recent experimental advances demonstrated control of the nuclear spins through microwave manipulation of the NV spin via dynamical decoupling ‘CPMG’ sequences. Here we show that more complex dynamical decoupling sequences improve the nuclear spin operations, i.e., gate fidelity, applicability range, and nuclear spin selectivity. We numerically show the efficacy of our method on NV centers in diamond, but our results are general and applicable to other types of defects in solids. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D08.00012: Time-optimal robust controls for Molmer-Sorensen gates in large ion chains Andre Carvalho, Claire Edmunds, Harrison Ball, Michael Hush, Michael Biercuk Performing high fidelity entangling operations in multi-qubit systems is an essential requirement for the scalability of quantum information processing. In trapped-ion architectures, these gates are achieved through external driving fields that excite shared oscillator modes: Molmer-Sorensen (MS) gates are a widely used example. In this talk, we present numerically optimized modulation protocols which enable the realization of pairwise MS interactions in long ion chains. We demonstrate how these protocols achieve efficient decoupling of the motional modes employed to effect the entangling operation and provide robustness against fluctuations in experimental parameters. We then demonstrate a routine for time-optimization of the gates on chains of up to 10 ions. The novel gates are not only more robust and faster than standard MS gates, but also more flexible in the choice of experimental parameters. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D08.00013: Probing the quantum nature of electronic transport by sub-nanosecond time-resolved measurements Jean Olivier Simoneau, Christian Lupien, Bertrand M Reulet Mesoscopic microwave measurements are usually carried out in the frequency domain. However, for some experiments involving large bandwidths (including frequency-resolved measurements) or short timescales (e.g. subcycle waveforms), the time domain can be a more suitable or convenient measurement framework.[1] |
Monday, March 2, 2020 5:06PM - 5:18PM |
D08.00014: Optimizing pulses with geometric parameters for dynamically-corrected single qubit gate Xiuhao Deng We used geometric parametrization to solve for the constraints of the control pulses to implement dynamically-corrected single qubit gate for superconducting qubits. We considered errors due to: I) crosstalk with other qubits; II) strong coupling to TLS defect; III) coupling to low frequency noisy background, and so on. The errors to be corrected are modeled in perturbative and non-perturbative regime respectively, resulting in different geometric parameters. The pulses obtained using geometric parametrization could corrected the errors and, furthermore, could be optimized in such parameter space with the number of parameters much less than discrete temporal parameter space associated with traditional quantum optimal control numerical approach such as GRAPE. Hence, our optimization approach performs much faster. We compare our optimized pulses with those generated with GRAPE, differential evolution, and other numerical approaches. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D08.00015: Robust and optimal control for SC qubits, two-qubit gates, and circuits Harrison Ball, Per Liebermann, André Carvalho, Harry Slatyer, Vicktor Perunicic, Rajib Chakravorty, Michael Hush, Michael Biercuk Superconducting quantum computers manifest distinct error processes at different levels of system complexity: from leakage or dephasing in individual transmon qubits to errors in two-qubit gates arising from dephasing, imperfect control signals, and unwanted cross-couplings. Quantum control at the physical-layer provides a pathway to combating these errors in today’s quantum hardware. In this talk we describe error modelling of dominant error channels in superconducting circuits relevant for parametrically-activated or cross-resonance gates. Advancing on previous work, we present optimal and robust controls that reduce sensitivity to both leakage and dephasing errors by orders of magnitude, as well as other optimized controls to reduce hardware errors at higher levels of system complexity. |
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