Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F08: Control and Modelling of Open Quantum Systems |
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Sponsoring Units: DQI Chair: Sophia Economou Room: 104 |
Tuesday, March 3, 2020 8:00AM - 8:12AM |
F08.00001: Experimental simulation of a two-level open system based on Trotter decomposition Xiaoxuan Pan, Jiaxiu Han, Weizhou Cai, Ling Hu, Yuwei Ma, Yuan Xu, Xianghao Mu, Changling Zou, Luyan Sun Quantum simulation is one of the promising applications on a fully controlled quantum system. Such tasks can be solved with either high dimensional ancillary systems or deep feedback control network. We demonstrate a hardware-efficient repetitive Trotter scheme of open system simulation, which allows efficient simulation of arbitrary noisy environments for a two-level system. The scheme only requires an ancillary superconducting qubit, and real-time feedback control is not necessary. We verify that our implementation can be further strengthened in two ways: higher-order Trotter operation sequencing and error mitigation, which are straight forward with the controllability of our system. Our results show the feasibility to perform quantum simulation tasks on small systems and with restricted experimental resources. |
Tuesday, March 3, 2020 8:12AM - 8:24AM |
F08.00002: Arbitrary quantum channel simulations of a superconducting qudit system Weizhou Cai, Jiaxiu Han, Ling Hu, Yuwei Ma, Yuan Xu, Xianghao Mu, Yipu Song, Chang-Ling Zou, Luyan Sun Unitary operations of closed quantum systems have been well studied. However, practical quantum systems are open and their evolution is described by quantum channels. So exploring arbitrary quantum channel simulation with minimum resources is of great importance for both fundamental understandings of open systems and mitigating of quantum noise. In this talk, we will introduce our recent experimental efforts on arbitrary quantum channel simulations of a high dimensional photonic qudit (cavity), with the assistance of a transmon qubit. First, continuous evolutions of an open quantum system are simulated by digitally and repetitively implementing Lindblad operators. Two interesting channels, odd parity stabilization channel and two-photon dissipation channel, have been demonstrated with this method. Then, the quantum channel that directly maps the input to output is simulated based on adaptive control. By using this method, preparation of arbitrarily mixed states and state tomography by symmetric informationally complete positive operator-valued measures are demonstrated. |
Tuesday, March 3, 2020 8:24AM - 8:36AM |
F08.00003: Adiabaticity in non-Hermitian dynamics of a superconducting qubit Weijian Chen, Maryam Abbasi, Mahdi Naghiloo, Yogesh Joglekar, Kater Murch In general, a quantum system subject to slow parameter variation will closely follow its instantaneous eigenstates. This well-known adiabatic theorem, however, has been shown to break down in recent studies of open systems with gain or loss. Such systems are effectively described by non-Hermitian Hamiltonians and thus possess complex eigenvalues and nonorthogonal eigenstates. In this talk, I will present our study of adiabaticity in non-Hermitian dynamics of a single dissipative superconducting qubit, where we tune the frequency and amplitude of microwave drives to vary the system Hamiltonian. The resulting dynamics is determined by the nonadiabatic coupling between eigenstates as well as their complex-eigenvalue-induced growth or decay. Our understanding of adiabaticity in the presence of complex eigenvalues will be important in harnessing non-Hermiticities for quantum sensing and control. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F08.00004: Encircling exceptional points of a single dissipative qubit Maryam Abbasi, Weijian Chen, Mahdi Naghiloo, scott Hershberger, Yogesh Joglekar, Kater Murch We study the behavior of a single dissipative qubit which is described by a non-Hermitian Hamiltonian. This system exhibits a degeneracy known as an exceptional point (EP) where both eigenvalues and eigenstates coalesce. According to the adiabatic theorem, slow variation of the system parameters in a closed loop transports the system back to its initial state. Surprisingly, in a loop enclosing an EP the eigenstates of the system will switch. Moreover, this behavior is chiral due to its dependence on the encircling direction and the initial state. We experimentally explore these phenomena by varying the drive parameters in a superconducting transmon circuit, creating closed loops in parameter space with one or two EPs. Our study shows how non-Hermiticities enable novel methods of quantum control. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F08.00005: Dissipative processs to generate entangled state in solid state system Wang Xin When the target system interacts with the environment with some dissipative process, this process may be engineered to generate and protect the quantum state. Dissipation can be used to engineer some strongly correlated state, and also help one to understand the dynamics of the system and reservoir. Former work has been completed to design the dissipation in many experimental system, for example, ion trap, superconductor and atomic ensembles system. We demonstrate firstly that by utilizing a designed dissipative protocol one can generate a maximum entangled state in Nitrogen-vacancy solid spin system. Meanwhile, the fidelity of target state will stay steady and not change with the generation sequence number increasing. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F08.00006: Shortcuts to adiabaticity in open systems: thermalization of an open quantum oscillator Aurelia Chenu, Leonce Dupays, Inigo Louis Egusquiza, Adolfo Del Campo The dynamical control of quantum systems is a necessity to advance quantum sciences and technology. Techniques known as shortcuts to adiabaticity (STA) provide an alternative to adiabatic driving, and have proven useful in a wide diversity of applications. However, they are currently restricted to the control of closed systems. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F08.00007: Modeling non-Markovian dynamics with augmented CPTP maps Kevin Young, Robin Blume-Kohout, Stephen D Bartlett Markovian quantum processes on qubits can be perfectly described with completely-positive, trace-preserving (CPTP) maps. However, real physical systems are replete with non-Markovian effects. Trapped ions experience heating, microwave sources display power instabilities, and resonators take time to relax. Fluctuating magnetic fields display large spatial correlations, qubits experience leakage, and quantum gates that occur early in a circuit can impact the performance of those occurring later. CPTP maps on qubits capture none of these memory effects. In this talk, we propose a family of augmented CPTP maps that enable simple models of a wide variety of non-Markovian dynamics. We provide a number of numerical examples demonstrating that that these maps are easy to construct and interpret. Furthermore, we show that we can estimate the parameters of these maps from experimental data. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F08.00008: Learning the dynamics of open quantum systems from local measurements Eyal Bairey, Chu Guo, Dario Poletti, Netanel Lindner, Itai Arad The increasing complexity of engineered quantum systems and devices raises the need for efficient methods to verify that these systems are indeed performing the desired quantum dynamics. Due to the inevitable coupling to external environments, these methods should obtain not only the unitary part of the dynamics, but also the dissipation and decoherence affecting the system's dynamics. Here, we propose a method for reconstructing the Lindbladian governing the Markovian dynamics of open many-body quantum systems, using data obtained from local measurements on their steady states. We show that the number of measurements and computational resources required by the method are polynomial in the system size. For systems with finite-range interactions, the method recovers the Linbladian acting on each finite spatial domain using only observables within that domain. We numerically study the accuracy of the reconstruction as a function of the number of measurements, type of open-system dynamics and system size. Interestingly, we show that couplings to external environments can in fact facilitate the reconstruction of Hamiltonians composed of commuting terms. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F08.00009: Noise Memory Kernel Reconstruction via the Post-Markovian Master Equation Haimeng Zhang, Daniel A Lidar Understanding and combating decoherence is one of the central topics in realizing quantum computation. Correlated, non-Markovian noise presents a particularly relevant challenge in superconducting qubit systems. This talk will present results on the construction of a bath memory kernel function from the experimentally measured state dynamics of a superconducting qubit. This phenomenological memory kernel arises in the post-Markovian master equation (PMME) [A. Shabani and D. A. Lidar, PRA 71, 020101 (2005)]. The memory kernel as constructed is of practical interest for quantum computation tasks as it provides insight into the noise origin and the characteristic timescales associated with bath memory effect. It also illuminates how the non-Markovian property of the noise can potentially be utilized to extend coherence timescales relative to the Markovian limit. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F08.00010: Scalable Bayesian learning of local Hamiltonians and Lindbladian Timothy Evans, Robin Harper, Steven Flammia As the size of quantum devices continues to grow, the development of scalable methods to characterise and diagnose noisy devices is becoming an increasingly important problem. Recent results demonstrate how a local Hamiltonians and Lindbladians can be reconstructed from a single, arbitrary steady state with a number of measurements that scales efficiently in the size of the system. These methods, however, can only characterise the system up to scalar factor and lack sufficient robustness to noise, both of which are imperative to be of practical use. In this talk I will present a Bayesian method that addresses both of these issues by making use of any, or all, of the following: experimental control of Hamiltonian couplings, the preparation of multiple states and the availability of any prior information we may already have for the Hamiltonian couplings. Moreover we provide an adaptive measurement protocol that can be performed online, updating estimates and their corresponding uncertainties as experimental data becomes available. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F08.00011: Parametric Quantum Noise Spectroscopy Using SchWARMA Kevin Schultz, Gregory Quiroz, David Clader Markovian noise is a fundamental assumption in many characterization and analysis protocols for quantum circuits. However, this assumption is generally not valid in reality, which has led to considerable efforts to characterize and alleviate temporally correlated errors. Here, we adapt techniques from classical time series analysis to model, simulate, and estimate non-Markovian noise. We call this family of techniques Schrodinger Wave ARMA (SchWARMA), and show that it is not only a flexible method for representing noise spectra, but that it is a powerful statistical model that can be used for estimating noise and predicting the effects of non-Markovian noise on quantum circuits. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F08.00012: Experimental Realization of Noise Injection using SchWARMA Andrew Murphy, Kevin Schultz, Jacob Epstein, Kyle P McElroy, Gregory Quiroz, Brian S Tien-Street, Joan Audrey Hoffmann, David Clader, Timothy Sweeney We develop a noise-injection scheme applied to an experimental qubit system in order to validate protocols that characterize and mitigate noise. We use a technique known as Schrodinger Wave Autoregressive Moving Average (SchWARMA) to mimic phase noise on a qubit. This is realized by imparting SchWARMA generated errors on the phase of the RF drive that is used to generate control pulses. The accumulation of phase errors mimics dephasing a qubit might experience relative to a perfect drive. We use quantum noise spectroscopy techniques to perform spectral estimation of the noise power spectrum and evaluate the efficacy of the noise injection approach. Our results show SchWARMA is a powerful tool for mimicking correlated phase noise processes in a superconducting qubit system. The power of SchWARMA can be shown to go beyond our initial experiments, extending to multi-axis noise models and arbitrary qubit systems. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F08.00013: Continuos feedback of a controllable nonlinear cavity with Deep Reinforcement Learning Riccardo Porotti, Michael Zwerger, Florian Marquardt Many tasks in quantum information processing require numerical methods to identify the best control sequence to achieve a specific goal. Deep Reinforcement Learning (DRL) has been applied with great success to many other fields, thanks to its ability to identify the best strategy in problems involving a competition between short and long-term rewards. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F08.00014: Quantum Machine Learning using a Dissipative Quantum Reservoir John Miller, Martha Villagran Recurrent neural networks (RNNs) are often slow learners, requiring extensive training of their hidden layers. In reservoir computing, the RNN's hidden layers are replaced by a reservoir, which can be a complex circuit (e.g., echo state network, or ESN) or physical system. The reservoir transforms recent temporal data into output patterns that can be read by a trainable single layer of neurons. The quantum reservoir, with just a few qubits and including dissipation, has recently been shown outperform a much larger classical ESN. Here we discuss the charge density wave (CDW) - a correlated electron-phonon system - as a candidate quantum reservoir. Some CDW materials (e.g., NbSe3) show learning, such as a pulse-duration memory effect, where 1-3 training pulses are needed experimentally vs. 100's to 1000's in classical simulations. This occurs in a highly dissipative environment with many normal electrons. Related materials (e.g., NbS3) have optimum CDW transport properties at room temperature, suggesting the possibility of certain types of quantum machine learning at high temperatures. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F08.00015: Decoherence Properties of Qubits and Oscillators Coupled to Minimal Environments Kevin Randles, David Diaz, Jean-Francois Van Huele, Ty Beus, Manuel Berrondo Decoherence refers to the loss of quantum coherence through contact with the environment. We are interested in characterizing this decoherence in models of simple quantum systems interacting with a minimal environment, following the work of Vidiella-Baranco [Physica A 402, 209 (2014) & Physica 459,78 (2016)]. We work out the full exact dynamics or approximations to the exact dynamics for coupled systems of qubits, oscillators, and mixed systems of qubits with oscillators. We then trace over the environment degrees of freedom and extract the decoherence of the reduced system as characterized by its linear entropy and visualize the results with Bloch spheres and Husimi functions. We relate decoherence rates to coupling strength. We also observe similarities and differences between solutions for couplings corresponding to the rotating and counter-rotating wave approximations. We notice in particular the disappearance of periodicity above a critical coupling strength in the counter rotating coupling in the oscillator case. |
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