Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session K09: General Quantum InformationLive
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Chair: Asier Piniero, JILA |
Wednesday, June 2, 2021 10:30AM - 10:42AM Live |
K09.00001: Faster State Preparation by Controlled Quantum Dynamics from Reinforcement Learning Feng Chen, Shuai-Feng Guo Ground state transformation by crossing quantum phase transition can be achieved through adiabatic parameter change taking advantage of the inherent energy gap near quantum critical point from finite size effect of a many-body (MB) system. In real application scenarios, however, the efficacy of such an approach is compromised by the need to balance finite system lifetime with adiabaticity, as exemplified in a recent experiment that prepares three-mode balanced Dicke state near deterministically [1]. In this work, we employ reinforcement learning agent to optimize the tuning of quadratic Zeeman shift to control MB quantum dynamics for preparing balanced Dicke state. Benefiting from faster excited level dynamics, the learned non-monotonous control protocol facilitates much shorter sweeping time than previous protocols. Excluding atom loss, a theoretical fidelity ≥ 99% between prepared and the target Dicke state is achieved over a small fraction of the required time for adiabatic tuning. When loss is considered as a one-body stochastic effect, the RL agent remains effective by learning from the approximate dynamics based on the truncated Wigner method, leading to enhanced interferometric sensitivity within about half of the previously reported time. Implemented in a Bose-Einstein condensate of ∼104 87Rb atoms, the balanced three-mode Dicke state exhibiting an improved number squeezing of dB is prepared within 766 ms, highlighting the potential of RL for quantum dynamics control and quantum state preparation in interacting MB systems [2]. |
Wednesday, June 2, 2021 10:42AM - 10:54AM Live |
K09.00002: Quantum state engineering by shortcuts-to-adiabaticity Obinna Abah, Ricardo Puebla, Mauro Paternostro We present a fast and robust framework to prepare non-classical states of a bosonic mode exploiting a coherent exchange of excitations with a two-level system ruled by a Jaynes-Cummings interaction mechanism. Our protocol, which is built on shortcuts to adiabaticity, allows for the generation of arbitrary Fock states of the bosonic mode, as well as coherent quantum superpositions of a Schro ¨dinger cat-like form. In addition, we show how to obtain a class of photon-shifted states where the vacuum population is removed, a result akin to photon addition, but displaying more non- classicality than standard photon-added states. Owing to the ubiquity of the spin-boson interaction that we consider, our proposal is amenable for implementations in state-of-the-art experiments. |
Wednesday, June 2, 2021 10:54AM - 11:06AM Live |
K09.00003: Bloch sphere description of multi-level systems: Chern number and state tomography Cameron Kemp, Nur Unal The geometric interpretation of spin 1/2 systems on the Bloch sphere S2 is well established in different areas across condensed matter physics and quantum information. These descriptions not only provide a visual aid for capturing various phenomena, but are also useful in bridging abstract concepts from mathematics to reveal hidden connections, such as novel topological relations, in experiments. Although such notions are known in mathematics for larger Hilbert spaces, beyond spin 1/2 they have been so far favored less for practical usage in condensed matter. By extending this geometric description to multi-band models, we characterize their dynamics on the higher dimensional Bloch sphere. We show that the topological properties such as the Berry curvature exhibit simple forms in terms of the coherence vector which is the object of interest on the Bloch sphere. We reveal an effective two-level description for the Chern number hidden among multi bands. We also present a tomography scheme to extract the coherence vector of the state in quantum simulation experiments via simple quenches, which gives access to these geometrical and topological properties by constructing the full wave function. |
Wednesday, June 2, 2021 11:06AM - 11:18AM Live |
K09.00004: Drone-based Quantum Key Distribution (QKD) Samantha Isaac, Andrew Conrad, Roderick Cochran, Daniel E Sanchez-Rosales, Akash Gutha, Tahereh Rezaei, AJ Schroeder, Hudson Jones, Brian Wilens, Daniel J Gauthier, Paul G Kwiat Due to their effortless reconfigurability, expanded accessibility, rapid deployment, and capacity to traverse versatile environments, Unmanned Aerial Vehicles (UAVs) have seen increased utilization across numerous industries, leading to various novel applications. These range between law enforcement, disaster relief, consumer deliveries, and geographic mapping, with new applications continually appearing. With a growing demand for UAV-based services comes a growing concern for the safety and security of UAV operations. In contrast to classical approaches, quantum communication protocols provide the ability to transmit provably secure messages. Current quantum cryptography implementations focus on fiber-based or fixed free-space point-to-point channels. We seek to develop the emerging technology of UAVs to realize a free-space optical quantum channel that can exchange quantum-secured random keys over distances up to 10 km between two drones in flight. Here, we present progress on the development and deployment of the QKD source and the Pointing, Acquisition and Tracking (PAT) system, while overcoming the challenges presented by the Size, Weight, and Power (SWaP) constraints of the drone. Preliminary results yield a table-top Quantum Bit Error Rate (QBER) of 7.5% along with an in-flight classical channel loss of 20.6 dB. Mobile free-space quantum-secured communication platforms are an integral part of developing an expansive quantum communication network. |
Wednesday, June 2, 2021 11:18AM - 11:30AM Live |
K09.00005: Quantum Science with Ytterbium Atom Arrays Alex Burgers, Samuel Saskin, Jack Wilson, Shuo Ma, Jeff D Thompson Arrays of neutral atoms trapped in optical tweezers are a leading architecture for quantum simulation and quantum computing protocols. Alkaline-earth atoms offer many potential advantages including extremely long nuclear spin coherence times for quantum information storage and narrow optical transitions for use in efficient laser-cooling, metrology and precision measurement. We describe our progress using Yb atoms trapped in reconfigurable, magic-wavelength (532 nm) optical tweezers. We achieve high atom detection fidelity by simultaneously cooling and imaging on the 1S0 - 3P1 transition [1]. We can then drive Rydberg excitations to investigate interactions in the atom array. In contrast to previous experiments where the traps are turned off during Rydberg excitation to avoid loss, we show that atoms in the Rydberg state can be stably trapped in our optical tweezers by leveraging the polarizability of the Yb+ core thus improving versatility and extending the lifetime for interactions [2]. We will also discuss ongoing efforts to realize highly coherent Rydberg operations and the use of the 171Yb nuclear spin qubit. |
Wednesday, June 2, 2021 11:30AM - 11:42AM Live |
K09.00006: Observing a dynamical purification phase transition in a trapped-ion quantum computer Crystal Noel, Pradeep Niroula, Marko Cetina, Daiwei Zhu, Andrew Risinger, Laird Egan, Debopriyo Biswas, Alexey V Gorshkov, Michael Gullans, David A Huse, Christopher R Monroe We report on experimental studies of a novel error correction threshold called a “purification transition” that occurs as we tune the rate of measurement during random unitary dynamics. We use a single reference qubit entangled with the larger system to efficiently study the purification dynamics. We probe the two phases by sampling hundreds of instances of random circuits using a quantum computer with 13 trapped 171Yb+ ions as the qubits. Sampling the large subset of circuits requires calibrations and circuit running on long timescales with high fidelity. On the accessible circuit depths and system sizes, we find conclusive evidence of the different phases and show numerically that, in the limits of longer circuits and moderately larger system sizes, critical properties of the purification transition emerge. |
Wednesday, June 2, 2021 11:42AM - 11:54AM Live |
K09.00007: Entanglement swapping of noisy qubits Vladimir Malinovsky, Mark Hillery, Dov Fields, Siddhartha Santra, Janos A Bergou Entanglement swapping is a basic protocol in quantum network operations and other quantum information processing applications based on entanglement distribution. Here we present a comprehensive analysis of entanglement swapping of noisy qubits using concurrence as a measure of entanglement. We examine entanglement swapping of qubit pairs in Schmidt bases and discuss relations between concurrences of the input and output states. |
Wednesday, June 2, 2021 11:54AM - 12:06PM Live |
K09.00008: Maximum efficiency of general two qubit linear-optical state analyzers Dov Fields, Mark Hillery, Janos A Bergou, Vladimir Malinovsky Linear optics is a critical technology for quantum information due to its reliability and ease of implementation. However, despite these advantages, linear optics is hampered by the limited set of total possible operations that can be performed with linear optical setups. While it has been shown that any general transformation can be performed on a optical system using only linear optics, these setups only succeed with some probability. In general, determining the optimal approach to implementing a linear optical operation is an extremely non-trivial task. In this paper, we specifically focus on the problem of measuring two qubit states in an arbitrary basis. For entangled basis states, such as the Bell-states, a perfect state analyzer is impossible. When we restrict our analysis to not allowing any auxiliary photons to be used in the discrimination process, we are able to derive that it is not possible to discriminate unambiguously any arbitrary basis of entangled two-qubit states with a probability higher than 50%. This is a generalization upon the previously known only for the Bell basis. Additionally, we specifically consider how to achieve the optimal unambiguous discrimination of bell-like states. We derive a general method for discriminating between bell-like states with a success rate of 25%. |
Wednesday, June 2, 2021 12:06PM - 12:18PM Live |
K09.00009: Protocol to measure the out-of-time-ordered correlator at finite temperature Bhuvanesh Sundar, Andreas Elben, Lata Kh Joshi, Torsten Zache Information scrambling, which is the spread of local information through a system's degrees of freedom, is an essential feature of many-body dynamics. In quantum systems, this scrambling is captured by the out-of-time-ordered correlator (OTOC). In this talk, we present an experimentally feasible protocol to measure the OTOC for an analog quantum system at a finite temperature. We numerically demonstrate that our protocol is robust against realistic noise for moderate system sizes. We show that the OTOC has a nontrivial temperature dependence which can be straightforwardly measured in experiment. Measuring the OTOC at finite temperature will provide crucial data to test rigorous predictions made for information scrambling in chaotic systems, as well as help probe regimes away from it. |
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