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 G73: Scaling Error MitigationFocus
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Sponsoring Units: DQI Chair: Zoe Gonzalez Izquierdo, USRA - Univ Space Rsch Assoc Room: Room 405 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G73.00001: Purification-based quantum error mitigation of pair-correlated electron simulations Thomas E O'Brien, Gian-Luca Anselmetti, Fotios Gkritsis, Vincent E Elfving, Stefano Polla, William J Huggins, Oumarou Oumarou, Kostyantyn Kechedzhi, Christian Gogolin, Ryan Babbush, Nicholas C Rubin An important measure of the development of quantum computing platforms has been the simulation of increasingly complex physical systems. Prior to fault-tolerant quantum computing, robust error mitigation strategies are necessary to continue this growth. Here, we study physical simulation within the seniority-zero electron pairing subspace, which affords both a computational stepping stone to a fully correlated model, and an opportunity to validate recently introduced ``purification-based'' error-mitigation strategies. We compare the performance of error mitigation based on doubling quantum resources in time (echo verification) or in space (virtual distillation), on up to 20 qubits of a superconducting qubit quantum processor. We observe a reduction of error by one to two orders of magnitude below less sophisticated techniques (e.g. post-selection); the gain from error mitigation is seen to increase with the system size. Employing these error mitigation strategies enables the implementation of the largest variational algorithm for a correlated chemistry system to-date. Extrapolating performance from these results allows us to estimate minimum requirements for a beyond-classical simulation of electronic structure. We find that, despite the impressive gains from purification-based error mitigation, significant hardware improvements will be required for classically intractable variational chemistry simulations. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G73.00002: Improving algorithmic performance of tunable superconducting qubits using deterministic error mitigation Varun Menon, Pranav S Mundada, Aaron Barbosa, Yuval Baum The largest NISQ era devices currently available utilise superconducting architectures. Flux tunable superconducting qubits in particular help avoid frequency collisions in large devices, and can utilize fast gates and measurement schemes. However, such architectures are affected by higher sensitivity to flux noise that affects gate fidelities, in addition to decoherence and readout errors that inhibit the performance of all NISQ era devices, leading to sub-optimal accuracy on even few qubit algorithms. In this work, we show how our deterministic error mitigation pipeline improves the performance of superconducting hardware on algorithmic benchmarks. In particular, we utilize intelligent quantum compilation and physics-aware circuit layout selection strategies, optimized single and two qubit gate calibration, measurement readout error mitigation, and correlated dynamical decoupling, to reduce errors at every stage of the quantum hardware stack. We demonstrate these methods on a Rigetti quantum computer, and show over a 1000 X and 30 X improvement in accuracy on 15 qubit Bernstein Vazirani and 7 qubit Quantum Fourier Transform circuits respectively. We also show that our calibration methods efficiently improve single and two qubit gate fidelities across the device, leading to improvements of more than 7 X over default fidelities. We also show that our methods suppress idling errors and crosstalk across the device, leading to a significant increase in quantum volume of the quantum computer. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G73.00003: Probabilistic error cancellation for measurement-based circuits Riddhi Swaroop Gupta, Ewout van den Berg, Kristan Temme, Abhinav Kandala Probabilistic error cancellation (PEC) is a practical error-mitigation technique to obtain accurate, bias-free estimates of observable expectation values. The procedure learns the noise associated with ideal unitary gates and implements a noise inversion via probabilistically sampling Paulis from an appropriately constructed inverse distribution. In this work, we extend the PEC framework to move beyond ideal unitary gates and implement noise learning and mitigation for circuits consisting of mid-circuit measurements, and classically controlled unitary operations ('feedforward'). Our work introduces a novel approach to learning and error mitigation for circuits with non-unitary, mid-circuit operations as well as characterizing the impact of these operations on active, unmeasured qubits. We discuss the learned measurement model for mid-circuit measurements and feedforward, and comparatively analyze several methods for constructing and solving the underlying inverse problem. The learning protocol retains the scalability of the approach introduced in [arXiv:2201.09866] and can be extended to circuits with large qubit count. These advances enable us to demonstrate PEC on measurement-based circuits. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G73.00004: Hardware Acceleration for Randomized Gate Execution Andrew D Patterson, Andrew T Arrasmith, Marco Paini NISQ era devices can make use of randomized gate sampling to improve results in the near-term. For example, known error mitigation techniques such as randomized compiling and algorithms such as projected quantum kernel methods make use of these. Current control system interfaces often lack the ability to implement such techniques at an optimal rate due to latency and other overheads in configuration of the control stacks, which are rather optimized for repetition of identical programs in a simple loop. Extending such a loop to include randomized gate executions may provide performance improvements to the aforementioned techniques, making them practical for real-world applications. In this talk, control systems suitable for running these methods will be discussed. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G73.00005: Experimentally characterizing error mitigation on large quantum circuits Andrew Eddins, Youngseok Kim, Ewout van den Berg, Xuan Wei, Sergey Bravyi, Kristan Temme, Abhinav Kandala Quantum error mitigation may provide a path to quantum advantage even on near term processors that lack fault tolerance. Error mitigation techniques can cancel the noise-induced bias in expectation values by sacrificing precision (variance). This variance can be suppressed by paying a sampling time cost, but this cost grows exponentially in circuit area, sharply limiting the maximum viable circuit size at current hardware error rates. Optimal performance thus hinges on an understanding of the available bias-variance trade space. Methods such as zero-noise extrapolation that suppress rather than null the bias may in principle enlarge the maximum viable circuit, but implementations often rely on strong assumptions about underlying device behavior, and how to optimize performance at scales beyond exact classical simulability remains a subject of research. Here we use a 65-qubit processor to experimentally characterize the performance and cost of mitigating circuits at scale by benchmarking accuracy on verifiable Clifford circuits, and discuss extensions to non-Clifford circuits. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G73.00006: Hardware Acceleration of Near-Term Quantum Computation Andrew T Arrasmith, Andrew D Patterson, Alice Boughton, Marco Paini Achieving a practical computational advantage with near-term quantum computers will require contending with hardware errors, likely through a combination of a carefully chosen application and the use of techniques to mitigate errors. A number of both possible near-term applications and error mitigation techniques have been demonstrated, but there is still an open question about the practicality of these approaches given both practical limitations to these methods as well as the execution time required to enact them. Here we will discuss how using advanced control system techniques at runtime may speed up and improve the performance of near-term quantum computation. |
Tuesday, March 7, 2023 12:42PM - 1:18PM |
G73.00007: Recent progress and challenges in error mitigation with fixed-frequency superconducting quantum processors Invited Speaker: Youngseok Kim Superconducting quantum processors have recently made tremendous improvements in both quality and scale. Concurrent progress in error mitigation techniques has now enabled the application of these to quantum circuits at scales beyond exact classical simulation. In this talk, I will first discuss experimental challenges for large fixed frequency superconducting processors and present strategies towards tailoring the noise for error mitigation. I will then discuss our recent progress towards experimental implementations of zero noise extrapolation on a 65 qubit processor. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G73.00008: Eliminating overhead: Improving the performance of hybrid algorithms using deterministic error suppression Smarak Maity, Pranav S Mundada, Aaron Barbosa, Tom Merkh, Andre Carvalho, Michael Hush, Michael Biercuk, Yuval Baum Large-scale fault-tolerant quantum computers will enable new solutions for problems known to be hard for classical computers. While scalable and fault-tolerant quantum computers are currently out of reach, hybrid quantum-classical algorithms provide a path towards achieving quantum advantage for certain types of optimization problems on NISQ devices. Errors and imperfections in existing quantum computers degrade the performance of these algorithms. Various statistical techniques have been used to address this issue, including zero noise extrapolation and random compilation methods such as Pauli twirling. These techniques introduce additional sampling overhead, increasing the hardware execution time required to complete the tasks. In this talk, we show that a deterministic error suppression workflow improves the performance of hybrid algorithms on currently available quantum hardware. This is done by improving the performance of arbitrary quantum circuits on the hardware, without introducing any additional overhead. We demonstrate the effectiveness of our tools via the implementation of QAOA and VQE on real devices. Our workflow improves the structural similarity index (SSIM) of the energy landscape (compared to the ideal landscape) by 28x for a 5-qubit QAOA problem, and improves the mean energy deviation (from the ideal energy) by 5x for a 6-qubit VQE problem. In this way, our methods render non-working algorithms into useful ones, while keeping the required hardware time low. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G73.00009: Error suppression and error mitigation using Qiskit Runtime Pedro Rivero State of the art quantum computers are noisy in every possible way, which threatens out ability to produce meaningful results out of this nascent technology in the short term. Classical computing has a way of dealing with this sort of scenario which has been proven to work over decades of daily usage: error correction. Unfortunately, correcting quantum computations is not as straight forward as classical ones, and it requires either the baseline noise to be smaller than what is offered by current capabilities, or a vast amount of physical qubits. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G73.00010: Probing the effect of superconducting gap profile on quasiparticle dynamics in superconducting qubits Spencer Diamond, Heekun Nho, Thomas Connolly, Pavel Kurilovich, Valla Fatemi, Michel H Devoret Single-charge tunneling is a decoherence mechanism affecting superconducting qubits. Suppressing the flux of high-energy photons reduces the rate of single-charge tunneling in these devices; however, there remains a nonequilibrium quasiparticle population due to undetermined Cooper-pair breaking mechanisms. We have found that these nonequilibrium quasiparticles are well-thermalized and become trapped in regions of the device with a lower superconducting gap. We measure single-charge tunneling rates in devices with different engineered superconducting gap profiles placed in a shared photon environment. This results in an improved understanding of the effect of superconducting gap profile on the spatial distribution and dynamics of quasiparticles in superconducting qubits. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G73.00011: Assessing phonon trap efficiency through on-chip spatial and energy resolved detection of high energy impacts Anil Murani, Francesco Valenti, Patrick Paluch, Nicolas Gosling, Thomas Reisinger, Robert Kruk, Robert Gartmann, Richard Gebauer, Oliver Sander, Ioan-Mihai Pop High energy ionizing impacts (muons, gamma rays, etc.) on a chip convert to high energy phonons which can propagate over large distances in the substrate, breaking Cooper pairs in superconducting devices on their way. These impacts are detrimental for quantum computing as they can produce correlated errors, a critical pitfall for current quantum error correction schemes. Mitigating these impacts can be done e.g. through shielding or on-chip phonon traps. Being able to detect high energy impacts and quantify the efficiency of phonon traps is therefore of paramount importance for superconducting quantum processors. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G73.00012: Suppression of Correlated Qubit Errors by Silicon Micromachining Matthew Snyder, Matthew Snyder, David C Harrison, Chuan-Hong Liu, Sohair Abdullah, Shravan Patel, Chris D Wilen, Vito M Iaia, Britton L Plourde, Robert McDermott Recent work has demonstrated that high-energy particle impacts result in phonon-mediated quasiparticle poisoning and correlated errors in superconducting qubits. This poses a problem for error correction codes, which generally assume uncorrelated errors. In this work, we investigate suppression of these errors by using a deep reactive ion etch process to modify the propagation of pair-breaking phonons in the qubit substrate. We utilize three distinct approaches. In the first, we incorporate an array of scattering centers to suppress ballistic phonon propagation. In the remaining two approaches, we define phonon bottlenecks and moats to acoustically decouple individual qubits from their neighbors. We use direct injection of quasiparticles from SIS junctions arrayed around the chip perimeter to generate a high flux of pair-breaking phonons. We compare the rates of correlated relaxation events and charge-parity switches in these devices to baseline data from devices with no mitigation. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G73.00013: Decoherence Suppression in Transmon Qubits by Encapsulation in Hexagonal Boron Nitride Sohair Abdullah, David C Harrison, Robert McDermott, Abigail Shearrow, Chuan-Hong Liu Magnetic surface adsorbates are a dominant contributor to qubit dephasing from 1/f flux noise. At the same time, surface adsorbates can act as strongly coupled two-level state (TLS) defects, leading to strong enhancement of the qubit energy relaxation rate at discrete operating frequencies. Here we describe an approach to reduce decoherence that involves encapsulation of transmon qubits in few-layer hexagonal boron nitride (hBN). The inert hBN membrane is expected to inhibit nucleation of microscopic adsorbates that induce both dephasing and relaxation, without contributing additional loss. We describe two series of experiments to probe the effectiveness of hBN encapsulation at reducing decoherence. First, we perform T1 swap spectroscopy to map out the spectrum of strongly-coupled TLS defects for devices with and without hBN encapsulation. Next, we use single-shot Ramsey tomography to extract the power spectral density of magnetic flux noise for both encapsulated and reference devices. These results shed light on the microscopic sources of qubit decoherence. We discuss prospects for extending this technique to larger multiqubit arrays. |
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