Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S33: Novel Quantum Control TechniquesLive
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Sponsoring Units: DQI Chair: Aurelia Chenu, University of Luxembourg |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S33.00001: Rescaled time, shortcuts to adiabaticity, and Dirac dynamics AGNIVA ROYCHOWDHURY, Sebastian Deffner Shortcuts to adiabaticity are a prominent tool-kit from quantum control to achieve effectively adiabatic dynamics in finite time. In this work, we explore both classical and quantum variants of shortcuts from so-called time-rescaled dynamics. We prove that time-rescaled Schrodinger systems and its classical variants with scale-invariant potentials can be reduced to time-independent problems with a modified scale-invariant potential. We also show that Hamiltonians, containing time-dependent kinetic terms in multi-dimensional Dirac systems like ultracold atoms, graphene and Weyl semi-metals, can be controlled and have their time-dependence modified by using external parameters in additional driving potentials. Our work opens up new avenues to realize shortcuts to adiabaticity in systems where the dynamics may have complicated dependence on time. |
Thursday, March 18, 2021 11:42AM - 11:54AM Live |
S33.00002: Shortcuts to adiabatic pumping in classical stochastic and non-Hermitian systems Ken Funo, Neill Lambert, Franco Nori, Christian Flindt We consider adiabatic charge pumping in classical stochastic and non-Hermitian systems. If two control parameters are periodically and slowly modulated in time, it is known that the pumped charge contains a geometric contribution in addition to a dynamical one. In this adiabatic regime the geometric contribution is important because it enables non-zero charge pumping even at zero bias. Here, we make use of recent advances in shortcuts-to-adiabaticity to construct a control protocol which enables this geometric pumping to operate well beyond the adiabatic regime. We explicitly show that the pumped charge for the controlled dynamics is exactly given by the dynamic and geometric contributions [1]. |
Thursday, March 18, 2021 11:54AM - 12:06PM Live |
S33.00003: Engineering fast high-fidelity bias-preserving gates on stabilized cat qubits Qian Xu, Joseph Iverson, Fernando Brandao, Liang Jiang It has been recently proposed that cat qubits, which possesses a biased noise channel, can be stabilized in a driven Kerr oscillator. A set of gates on the cat qubits, including a controlled-NOT gate, can be constructed in a way that preserves the noise bias. In the presence of photo loss, the gates have to be implemented fast in order to obtain high gate fidelity. However, as the gate speed increases the non-adiabaticity of the gates causes leakage from the codespace, which after being projected back induces the minor type of error and destroys the noise bias. We show that adding additional engineered two-photon dissipation helps suppress the minor type of error but enhances the major type of error at the same time. To address this problem, we apply shortcuts to adiabaticity (STA) methods to the originally proposed gates to suppress the non-adiabatic errors so that additional two-photon dissipation during the gate implementation is no longer in need. We show that using the improved control scheme we can obtain higher gate fidelity and higher noise bias simultaneously in the presence of a realistic level of noise, which can significantly reduce the resource overhead required for concatenating the cat qubits with a second level of coding to implement concatenated error correction. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S33.00004: Quantum Control via Enhanced Shortcuts to Adiabaticity Anthony Kiely Fast and robust quantum control protocols are often based on an idealized approximate description of the relevant quantum system. While this may provide a performance that is close to optimal, improvements can be made by incorporating elements of the full system representation. We propose a technique for such scenarios, called enhanced shortcuts to adiabaticity (eSTA). The eSTA method works for previously intractable Hamiltonians by providing an analytical correction to existing STA protocols. This correction can be easily calculated, and the resulting protocols are outside the class of STA schemes. We demonstrate the effectiveness of the method for different cases. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S33.00005: Geometric filter function approach to dynamically corrected gates that suppress time-dependent noise Bikun Li, Fernando. A. Calderon-Vargas, Junkai Zeng, Edwin Barnes We present a geometric filter function method for designing smooth control pulses that dynamically correct time-dependent noise errors. Under this framework, robust qubit evolution is mapped to geometric curves that satisfy certain constraints that guarantee the suppression of the leading-order error. We use the damping Newton method to numerically solve the constraints, obtaining a series of polynomial-like solutions that produce pulses for a range of single-qubit gates. Several of these pulses are not only non-negative but also have the advantage of relatively low bandwidth and amplitude. These features make the pulses experimentally feasible for platforms like semiconductor quantum dot spin qubits or superconducting qubits by respecting hardware and pulse generation constraints. We also provide simulation results of our pulses against different types of time-dependent noise. We find high fidelities across a range of noise parameters, demonstrating the effectiveness of this approach. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S33.00006: Noise-resistant Landau-Zener sweeps design from geometrical formalism Fei Zhuang, Junkai Zeng, Edwin Barnes, Sophia Economou A newly discovered geometric formalism is a promising approach for designing dynamically corrected gates. In this formalism, the evolution of a qubit under drive and noise is in one-to-one correspondence with a 3D space curve. We exploit this correspondence to design noise-robust Landau-Zener-style sweeps through an avoided crossing. In the case where the avoided crossing is purely noise-induced, we demonstrate multiple phase gates that are error-robust up to the 2nd order. In the general case, where avoided crossings are not just from noise, we arrive at a robust sweeping protocol for gate design through a technique we introduce for building closed 3D space curves with the desired properties. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S33.00007: Tailored quantum simulation with analog control optimization Paul Kairys, Travis S Humble Analog quantum simulation offers a highly efficient, hardware-specific approach to studying quantum dynamics in which external control of a device Hamiltonian simulates the dynamics of a target system. However, identifying the controls necessary to simulate a given target system varies with the physics of the device and goal of the simulations. We apply quantum optimal control theory to compile hardware-level controls that drive quantum dynamics of the Bose-Hubbard system within a model circuit-QED Hamiltonian. Our approach uses the GOAT algorithm in the presence of practical control constraints including bandwidth, geometry, and multi-level Hamiltonians to construct optimal controls that simulate time-dependent dynamics of the target system. We evaluate the accuracy and robustness of these controls using a series of numerical simulations. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S33.00008: Stochastic action principle for Gaussian states of a simple harmonic oscillator Tathagata Karmakar, Philippe Lewalle, Andrew N Jordan Subjecting an oscillator to continuous weak measurements is an integral part of quantum control and feedback. In my presentation, I will describe the application of Chantasri-Dressel-Jordan formulation (CDJ) of stochastic action principle for a quantum simple harmonic oscillator under weak position and momentum measurements. The selection of such a system paves the way to extend the CDJ formalism to infinite-dimensional systems. Using the preservation of Gaussianity of a state under Gaussian weak measurement, it is possible to find the stochastic Hamiltonian, stochastic trajectories, and the equations for optimal paths of the system. I will also describe the analytical solutions and behavior of the optimal paths under reasonable approximations. Finally, my presentation will delve into the energetics of the measurement process using the optimal path description. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S33.00009: Semi-Analytic Method for Rapid Simulation and Optimization of Driven Quantum Systems Ross Shillito, Jonathan Gross, Agustin Di Paolo, Elie Genois, Alexandre Blais The controls that are used to enact logical operations on qubits and cavities in circuit QED are described by time-dependent Hamiltonians that often include rapid oscillations. In order to fully capture these fast time dynamics in numerical calculations, a very small integration time step is required. In practice, this can be performance intensive impacting the simulation time and memory requirements. In this work, we present a semi-analytic method based on a Dyson expansion for arbitrary time-dependent quantum systems with a diagonal circuit Hamiltonian. This method captures the entire dynamics of the highly oscillatory terms of the Hamiltonian, reducing sensitivity to the chosen step size and providing significant performance improvements over current numerical integrators. This approach also returns the analytic derivative with respect to the drive strength amplitudes, which allows for rapid optimization with routines such as GRAPE to return high fidelity gates. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S33.00010: Numerical Optimal Control of Open Quantum Systems N. Anders Petersson, Stefanie Guenther, Spencer Tomarken, Jonathan L DuBois We consider the ground state initialization problem for a superconducting (multi-level) qudit in a 3-D cavity, where the quantum system is modeled by Lindblad's master equation. This is an optimal control problem, which aims to find control pulses that passively drive the qudit and the cavity to the ground state, independent of the initial state. To represent the control waveforms we use a flexible ansatz consisting of B-spline basis functions combined with carrier waves that trigger the known transition frequencies of the Hamiltonian. The objective of the optimization is to minimize a linear convex combination of the expected energy levels in each of the subsystems at the final time. Based on linearity, we can drive any initial state towards the desired final ground state through one superposition of basis states that spans all possible initial conditions; thus reducing the computational burden drastically. The optimization problem is solved iteratively using the L-BFGS algorithm combined with a projected line-search algorithm to satisfy amplitude bounds on the control functions. Numerical examples indicate that the reset time for a qudit can be significantly reduced compared to previous techniques. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S33.00011: Remote Addressing of Quantum Emitters with Chirped Pulses Silvia Casulleras, Carlos Gonzalez-Ballestero, Patrick Maurer, Juan Jose Garcia-Ripoll, Oriol Romero-Isart We theoretically demonstrate that chirped pulses propagating near a bandgap can be used to remotely address quantum emitters with sub-wavelength resolution. We introduce a particular family of chirped pulses that dynamically self-focus during their evolution in a medium with a quadratic dispersion relation. The state of a quantum emitter after the interaction with such pulses is highly sensitive to its position due to effective Landau-Zener processes induced by the pulse chirping. Our results propose pulse engineering as a powerful control and probing tool in the field of quantum emitters coupled to structured reservoirs. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S33.00012: Unraveling quantum and classical speed limits on observables Luis Garcia-Pintos, Adolfo Del Campo, Alexey V Gorshkov, Jason Green, Schyuler Nicholson We introduce speed limits to the evolution of observables of open quantum systems with arbitrary differentiable dynamics, generalizing the original derivation by Mandelstam and Tamm in 1945. The upper bounds on speed take the form of an uncertainty relation and unify previous bounds known for unitary quantum and for classical stochastic systems. By isolating the coherent and incoherent contributions to the system dynamics, we derive both lower and upper bounds to the speed of evolution, and prove that the latter provide tighter limits on the speed of observables than previously known quantum speed limits. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S33.00013: Optimizing feedback cooling for weakly monitored Bose-Einstein condensates Hilary Mayer Hurst, Shangjie Guo, Ian Spielman Weak measurement in tandem with real-time feedback control is a new route toward engineering novel non-equilibrium quantum matter. Here we develop a theoretical toolbox for quantum feedback control of Bose-Einstein condensates (BECs) using backaction-limited weak measurements in conjunction with spatially resolved feedback. In this talk, I focus on applying feedback via a single-particle potential, which prevents runaway heating that would otherwise result from measurement backaction. I present an analytical toy model for effective feedback cooling and compare different protocols with our stochastic GPE simulation results. Our results demonstrate that closed-loop quantum control of Bose-Einstein condensates is a powerful new tool for quantum engineering in cold-atom systems. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S33.00014: Measurement-driven navigation in many-body Hilbert space Yaroslav Herasymenko, Igor Gornyi, Yuval Gefen The challenge of preparing a system in a designated state spans various areas of quantum physics. To complete this task, one can employ quantum control through a sequence of generalized measurements. In an active version of this protocol, the obtained measurement readouts are used to adjust the protocol on-the-go, with a possibility for accelerated performance. |
Thursday, March 18, 2021 2:18PM - 2:30PM Live |
S33.00015: Proof of concept high energy physics application of superconducting radio frequency cavities for quantum computation: neutrino oscillation in free space and matter Joshua Job, Doga Kurkcuoglu, Steven Adachi, Gabriel Perdue We present results of a proof of concept application of superconducting radio frequency cavities for quantum computation in simulation in a high energy physics application, namely the oscillation of neutrino flavors in free space and matter. Using a simulation of the interaction of a transmon with the cavity, we design control pulses for the simulation of flavor oscillation and compare different techniques for the same, including decomposition into elementary SNAP and displacement gates and direct design of control pulses via gradient descent. We also discuss performance considerations and fidelity, as compared with classical simulation. Copyright 2020 Lockheed Martin Corporation |
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