Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session D03: Quantum Characterization, Verification, and ValidationLive
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Chair: Daniel Slichter, NIST Room: D135-136 |
Tuesday, June 2, 2020 2:00PM - 2:12PM Live |
D03.00001: Metastable qubits in trapped Calcium-43 ions Isam Moore, Jeremy Metzner, Alexander Quinn, David Wineland, David Allcock While all of the basic primitives required for universal \newline quantum computing (QC) have been demonstrated in trapped-ion qubits with high fidelity, it is currently not possible to simultaneously realize the highest achieved fidelities in a single ion species. This can be a serious impediment to the development of practical quantum computers. However, there are possibilities for achieving high-fidelity and full functionality in a single species with the use of multiple internallevels: augmenting existing species with new functionality. Specifically, essential dual-species capabilities can be developed in the Calcium-43$+$ ion through novel encoding schemes in metastable states, functions on demand (e.g. storage, coupling to motion, cooling, and state preparation and measurement). I will present simulation results and progress towards experimental implementation of high-fidelity preparation and readout procedures in metastable states of Calcium-43$+$. [Preview Abstract] |
Tuesday, June 2, 2020 2:12PM - 2:24PM Live |
D03.00002: Efficient Coherent Error Cancellation in Ion Trap Quantum Computers by Hidden Inverses Bichen Zhang, Ye Wang, Stephen Crain, Chao Fang, Dripto Debroy, Pak Hong Leung, Kenneth Brown, Jungsang Kim Quantum gates have errors that are both coherent and stochastic. Quantum error correcting codes are able to fix both types, however, coherent errors can often be suppressed by clever control. Instead of treating coherent errors and stochastic errors the same way, we can take advantage of the coherent properties to suppress systematic coherent errors. This is typically done with composite pulse sequences or dynamical decoupling that adds additional quantum gates. Here we show that by applying a simple technique we call hidden inverses, we can increase the fidelity of quantum simulation circuits in practice. Hidden inverses mitigate systematic over-rotations without increasing the overall operation complexity of the circuit. The experiment is conducted on a $^{171}$Yb$^+$ based quantum information processor with a surface trap. This work demonstrates that compiling quantum circuits using hidden inverse structure can improve fidelity without extra overhead. The technique can be combined with stabilizer codes to suppress coherent error and even combined with composite pulses. We are experimenting with other coherent error suppression methods at the circuit level including crosstalk cancellation and error detection codes. [Preview Abstract] |
Tuesday, June 2, 2020 2:24PM - 2:36PM Live |
D03.00003: Background free read out of trapped ion qubits David Hucul, Zachary S. Smith, William T. Grant, Paige Haas, Harris J. Rutbeck-Goldman, Boyan Tabakov, James A Williams, Carson F. Woodford, Kathy-Anne Brickman Soderberg Trapped barium 133 atomic ions are promising qubits for quantum information science. This radioisotope of barium requires only visible wavelengths for photoionization, laser-cooling, and the manipulation of a stable hyperfine qubit. The ideal energy level structure of this atomic ion has produced the lowest state preparation and measurement error of any qubit (1) and allows this qubit to be read out in a background free manner. Illumination of the ion produces atomic fluorescence at different wavelengths than the excitation light without mixing the atomic hyperfine clock qubit levels. Because the scattered light from the lasers can easily be separated from the atomic fluorescence with dichroic optics, barium 133 qubits can be integrated into optical fiber-based ion traps where all light delivery and collection is performed in the same optical fiber. This ``ion trap on a dipstick" makes barium 133 a natural candidate qubit for probing surfaces and coupling to superconducting qubits. The visible wavelengths and simplified operation of this qubit could also enable robust operation of multi-node trapped ion quantum networks. \\ (1). J.E. Christensen et al., arXiv:1907.13331 (2019). [Preview Abstract] |
Tuesday, June 2, 2020 2:36PM - 2:48PM Live |
D03.00004: Eliminating Leakage Errors in Hyperfine Qubits Daniel Stack, David Hayes, Bryce Bjork, Andrew Potter, Charles Baldwin, Russell Stutz Population leakage outside the qubit subspace presents a particularly harmful source of error that cannot be handled by standard error correction methods. Using a trapped Yb$^+$ ion, we demonstrate an optical pumping scheme to suppress leakage errors in atomic hyperfine qubits. The selection rules and narrow linewidth of a quadrupole transition are used to selectively pump population out of leakage states and back into the qubit subspace. Each pumping cycle reduces the leakage population by a factor of $\sim 3$, allowing for an exponential suppression in the number of cycles. We use interleaved randomized benchmarking on the qubit subspace to show that this pumping procedure has negligible side-effects on un-leaked qubits, bounding the induced qubit memory error by $\leq 2.0(8) \times 10^{-5}$ per cycle, and qubit population decay to $\leq 1.4(3) \times 10^{-7}$ per cycle. These results clear a major obstacle for implementations of quantum error correction and error mitigation protocols. [Preview Abstract] |
Tuesday, June 2, 2020 2:48PM - 3:00PM Live |
D03.00005: Experimental Observation of Hierarchy in Temporal Quantum Correlations HAO-CHENG WENG, CHEN-YEH WEI, HUAN-YU KU, SHIN-LIANG CHEN, YUEH-NAN CHEN, CHIH-SUNG CHUU The concepts of entanglement (or inseparability), steering, and Bell nonlocality form a logical hierarchy as manifested by the strict hierarchy of the entangled states, steerable states, and Bell-nonlocal states as well as the securities of the standard quantum key distribution (QKD), one-sided device-independent QKD, and device-independent QKD. In this work, we report the experimental observation of the hierarchy in their temporal analogues-- the temporal inseparability, temporal steering, and temporal CHSH inequality (or nonmacrorealism). These temporal quantum correlations, which quantify the two-time correlation of a quantum state with characterized or uncharacterized measurements, can exhibit distinct dynamics in quantum channels as a consequence of the hierarchy. Using the superconducting qubits provided by the IBM Quantum Experience, we observe the signature of the hierarchy in a depolarizing quantum channel while investigating the sudden death of these temporal quantum correlations. In addition, we also study how one may use these temporal quantum correlations to signify the non-Markovianity and benchmark the security of QKD. [Preview Abstract] |
Tuesday, June 2, 2020 3:00PM - 3:12PM Live |
D03.00006: Multimode Quantum State Tomography Andrew Dawes Measuring the quantum state of a weak beam of light presents numerous challenges. Using array detection in an unbalanced homodyne configuration, we demonstrate a technique capable of measuring simultaneously the quantum state of as many as 200 individual modes at the few-photon level. This technique is being developed with an eye toward applications in characterizing systems that implement optical memory and free-space optical communication. [Preview Abstract] |
Tuesday, June 2, 2020 3:12PM - 3:24PM On Demand |
D03.00007: High fidelity electron shelving for cw and background free state detection in 171Yb+ Conrad Roman, Anthony Ransford, Thomas Dellaert, Patrick McMillin, Wesley Campbell We present a method for improving state detection of $^{171}\text{Yb}^+$ hyperfine qubits through dissipative shelving of one qubit state to the metastable $^2\text{F}^o_{7/2}$ manifold. Narrowband optical pumping to the $^2\text{F}^o_{7/2}$ state is accomplished on the $^2\text{S}_{1/2}$ to $^2\text{D}_{5/2}$ electric quadrupole transition. With an extremely long lifetime ($\sim$ 5 years), shelved population is functionally disconnected from the detection cycle and off resonant effects during fluorescence detection are no longer limiting factors. We improve total state preparation and measurement fidelity in $^{171}\text{Yb}^+$ to 0.9999. Additionally, the optical separation after electron shelving allows for implementation of a novel background free state detection technique with resonant mode locked laser pulses, increasing the signal to noise during detection by more than two orders of magnitude in the presence of considerable laser scatter. [Preview Abstract] |
Tuesday, June 2, 2020 3:24PM - 3:36PM On Demand |
D03.00008: Continuous protection of a quantum state from motional dephasing Ofer Firstenberg We present a scheme for protecting a qubit from inhomogenous dephasing. The scheme relies on continuously dressing the qubit with an auxiliary state, which exhibits an opposite and potentially enhanced sensitivity to the same source of inhomogeneity. We study dressing configurations with either single or two drive fields. The latter offers robustness to drive noise, similarly to the double-dressing technique in continuous dynamical decoupling. We outline the minimal and optimal conditions for protection. As an experimental case study, we focus on motional dephasing of a spin wave in an atomic ensemble. We employ light storage and retrieval for quantifying the coherence time, which without protection is limited by the ballistic atomic motion at random velocities along the spin wave. When applying the protection scheme, the effect of the drive field can be understood as a velocity-dependent light shift, maintaining the correlations between position and phase of the spin wave. We demonstrate complete suppression of the inhomogeneous dephasing. Our scheme is applicable to various gas, solid, and engineered systems suffering from dephasing due to slow variations of conditions in either time, space, or other domains. [Preview Abstract] |
Tuesday, June 2, 2020 3:36PM - 3:48PM |
D03.00009: Single ion-qubit with coherence time over an hour Pengfei Wang, Chunyang Luan, Mu Qiao, Mark Um, Junhua Zhang, Ye Wang, Xiao Yuan, Mile Gu, Jingning Zhang, Kihwan Kim The coherence time of a single $^{\mathrm{171}}$Yb$^{\mathrm{+}}$ ion-qubit over 600 s has been reported with sympathetic cooling by a $^{\mathrm{138}}$Ba$^{\mathrm{+}}$ ion and optimized dynamical decoupling-pulses in an ambient magnetic field condition [1]. However, it was not clear what prohibits further enhancement. Here, we identify the limiting factors as ambient magnetic-field noise, phase noise and leakage of the microwave oscillator. With the experimental improvements, we observe over one hour of the coherence time for $^{\mathrm{171}}$Yb$^{\mathrm{+}}$ ion-qubit. In the experimental study, we adopt recently developed theories of coherence and use the best quantifier of the coherence and investigate the process of decoherence systemically. [1] Wang, Ye, et al. , Nature Photonics 11.10 (2017): 646-650. This work was supported by the National Key Research and Development Program of China under Grants No. 2016YFA0301900 and No. 2016YFA0301901 and the National Natural Science Foundation of China Grants No. 11374178, No. 11574002, and No. 11974200. [Preview Abstract] |
Tuesday, June 2, 2020 3:48PM - 4:00PM |
D03.00010: Hamiltonian Meta Learning Przemyslaw Bienias, Alireza Seif, Paraj Titum, Patrick Becker, Norbert Linke, Jiehang Zhang, Mohammad Hafezi Precise calibration of quantum devices is necessary for reliable quantum information processing. Full characterization and tuning a quantum system without making any assumption require resources that scale exponentially with the system size. Here, we assume a model for the noisy evolution of a quantum system, and by using a machine learning technique known as meta learning to train an optimizer that finds model parameters with less resources than other gradient based optimization algorithms. The training of our algorithm is done efficiently on smaller systems. However, the learned optimizer is transferable to larger systems. [Preview Abstract] |
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