We present a scheme for a reconstruction of states of quantum systems from incomplete tomographic-like data. The proposed scheme is based on the Jaynes principle of Maximum Entropy. We apply our algorithm for a reconstruction of motional quantum states of neutral atoms. As an example we analyze the experimental data obtained by the group of C. Salomon at the ENS in Paris and we reconstruct Wigner functions of motional quantum states of Cs atoms trapped in an optical lattice.
Generation of Motional Squeezed States for Neutral Atoms in Optical Tweezers
Institute for Molecular Science, National Institutes of Natural Sciences（国立自然科学研究所分子科学研究所）；Nanomaterials and Nanotechnology Research Center (CINN-CSIC), Universidad de Oviedo (UO)（阿斯图里亚斯自治区乌维多大学纳米材料与纳米技术研究中心）；Université Paris-Saclay, Institut d’Optique Graduate School, CNRS, Laboratoire Charles Fabry（巴黎萨克雷大学）；SOKENDAI (The Graduate University for Advanced Studies)（综合研究大学院大学）；RIKEN Center for Quantum Computing (RQC), RIKEN（理化学研究所）
The performance of many control tasks with Rydberg atoms can be improved via suppression of the motion-induced dephasing between ground and Rydberg states of neutral atoms. The dephasing often occurs during the {\it gap} time when the atom is shelved in a Rydberg state before its deexcitation. By using laser fields to induce specific extra phase change to the Rydberg state during the gap time, it is possible to faithfully transfer the Rydberg state back to the ground state after the gap. Although the Rydberg state transitions back and forth between different eigenstates during the gap time, it…
Isotope-agnostic motional ground-state cooling of neutral Yb atoms
Ludwig-Maximilians-Universität（慕尼黑大学）；Munich Center for Quantum Science and Technology (MCQST)（慕尼黑量子科学与技术中心）；Max-Planck-Institut für Quantenoptik（马克斯·普朗克量子光学研究所）
We study a scheme for implementing a controlled-Z (CZ) gate between two neutral-atom qubits based on the Rydberg blockade mechanism in a manner that is robust to errors caused by atomic motion. By employing adiabatic dressing of the ground electronic state, we can protect the gate from decoherence due to random phase errors that typically arise because of atomic thermal motion. In addition, the adiabatic protocol allows for a Doppler-free configuration that involves counterpropagating lasers in a $σ_+/σ_-$ orthogonal polarization geometry that further reduces motional errors due to Doppler shi…
High-fidelity non-adiabatic dark state gates for neutral atoms
Zentrum für Optische Quantentechnologien, Universität Hamburg（汉堡大学光学量子技术中心）；The Hamburg Centre for Ultrafast Imaging, Universität Hamburg（汉堡超快成像中心，汉堡大学）；UTC Quantum Center, University of Tennessee, Chattanooga（田纳西大学查塔努加分校UTC量子中心）
Motional Kerr-Cat States of an Atom in an Optical Tweezer
JILA, NIST and University of Colorado（JILA、美国国家标准与技术研究院和科罗拉多大学）；Department of Physics, University of Colorado（科罗拉多大学物理系）；Center for Theory of Quantum Matter, University of Colorado（科罗拉多大学量子物质理论中心）；Joint Center for Quantum Information and Computer Science, NIST and University of Maryland（量子信息与计算机科学联合中心、美国国家标准与技术研究院和马里兰大学）；Joint Quantum Institute, NIST and University of Maryland（量子研究所、美国国家标准与技术研究院和马里兰大学）；Institut Quantique, Université de Sherbrooke（舍布鲁克大学量子研究所）
Sustaining high-fidelity quantum logic in neutral-atom circuits via mid-circuit operations
Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China（中国科学技术大学现代物理系及微观尺度物质科学国家实验室）；Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学中科院量子信息与量子物理学前沿卓越中心上海分部）；Shanghai Research Center for Quantum Sciences（上海量子科学研究与创新中心）
We report on the state of the art of quantum walk experiments with neutral atoms in state-dependent optical lattices. We demonstrate a novel state-dependent transport technique enabling the control of two spin-selective sublattices in a fully independent fashion. This transport technique allowed us to carry out a test of single-particle quantum interference based on the violation of the Leggett-Garg inequality and, more recently, to probe two-particle quantum interference effects with neutral atoms cooled into the motional ground state. These experiments lay the groundwork for the study of dis…
Creating squeezed and non-classical collective motional many-body states through stroboscopic Rydberg dressing
Institut für Theoretische Physik and Center for Integrated Quantum Science and Technology, Universität Tübingen（蒂宾根大学理论物理研究所与集成量子科学技术中心）；Institute for Applied Physics, University of Bonn（波恩大学应用物理研究所）；RIKEN Center for Quantum Computing (RQC)（理化学研究院量子计算中心）；Physikalisches Institut and Center for Integrated Quantum Science and Technology, Universität Tübingen（蒂宾根大学物理研究所与集成量子科学技术中心）；School of Physics and Astronomy and Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems, The University of Nottingham（诺丁汉大学物理与天文学学院及量子非平衡系统数学与理论物理中心）
We present theoretical and experimental progress towards a new approach for the precision spectroscopy, coherent manipulation and state-to-state chemistry of single isolated molecular ions in the gas phase. Our method consists of a molecular beam for creating packets of rotationally cold neutrals from which a single molecule is state-selectively ionized and trapped inside a radiofrequency ion trap. In addition to the molecular ion, a single co-trapped atomic ion is used to cool the molecular external degrees of freedom to the ground state of the trap and to detect the molecular state using sta…
Long qubit coherence and efficient atom-photon coupling are essential for advanced applications in quantum communication. One technique to maintain coherence is dynamical decoupling, where a periodic sequence of refocusing pulses is employed to reduce the interaction of the system with the environment. We experimentally study the implementation of dynamical decoupling on an optically-trapped, spin-polarized $^{87}$Rb atom. We use the two magnetic-sensitive $5S_{1/2}$ Zeeman levels, $\lvert{F=2,\ m_{F}=-2}\rangle$ and $\lvert{F=1,\ m_{F}=-1}\rangle$ as qubit states, motivated by the possibility…
Fast and Coherent Transfer of Atomic Qubits in Optical Tweezers using Fiber Array Architecture
Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences（中国科学院精密测量科学与技术创新研究院武汉物理与数学研究所）；University of Chinese Academy of Sciences（中国科学院大学）
While the Rydberg-blockade regime provides the natural setting for creating $W$-type entanglement with cold neutral atoms, it is demonstrated here that a scalable entanglement resource of this type can even be obtained under completely different physical circumstances. To be more precise, a special instance of twisted $W$ states -- namely, $π$-twisted ones -- can be engineered in one-dimensional arrays of cold neutral atoms with Rydberg-dressed resonant dipole-dipole interaction. In particular, it is shown here that this is possible even when a (dressed) Rydberg excitation is coupled to the mo…
Multi-Qubit Parity Gates for Rydberg Atoms in Various Configurations
Parity Quantum Computing Germany GmbH（帕里量子计算德国有限公司）；Parity Quantum Computing GmbH（帕里量子计算有限公司）；Parity Quantum Computing France SAS（帕里量子计算法国公司）；Institute for Theoretical Physics, University of Innsbruck（因斯布鲁克大学理论物理研究所）
Fault-tolerant quantum computation with static atomic buses
University of Strasbourg（斯特拉斯堡大学）；CNRS（法国国家科学研究中心）；CESQ（量子化学中心）；ISIS（结构与成像研究所）；Department of Physics, University of Wisconsin-Madison（威斯康星大学麦迪逊分校物理系）；QPerfect SAS（QPerfect公司）；Institut Universitaire de France (IUF)（法兰西学院）；Infleqtion（Infleqtion公司）
Isolating neutral and charged particles from the environment is essential in precision experiments. For decades, this has been achieved by trapping ions with radio-frequency (rf) fields and neutral particles with optical fields. Recently, trapping of ions by interaction with light has been demonstrated. This might permit combining the advantages of optical trapping and ions. For example, by superimposing optical traps to investigate ensembles of ions and atoms in absence of any radiofrequency fields, as well as to benefit from the versatile and scalable trapping geometries featured by optical …
We propose a novel cooling scheme for realising single photon sideband cooling on particles trapped in a state-dependent optical potential. We develop a master rate equation from an ab-initio model and find that in experimentally feasible conditions it is possible to drastically reduce the average occupation number of the vibrational levels by applying a frequency sweep on the cooling laser that sequentially cools all the motional states. Notably, this cooling scheme works also when a particle experiences a deeper trap in its internal ground state than in its excited state, a condition for whi…
We investigate the dynamics of an ion sympathetically cooled by another laser-cooled ion or small ion crystal. To this end, we develop simple models of the cooling dynamics in the limit of weak Coulomb interactions. Experimentally, we create a two-ion crystal of Ca$^+$ and Al$^+$ by photo-ionization of neutral atoms produced by laser ablation. We characterize the velocity distribution of the laser-ablated atoms crossing the trap by time-resolved fluorescence spectroscopy. We observe neutral atom velocities much higher than the ones of thermally heated samples and find as a consequence long sym…
Optical atomic coherence at the one-second time scale
由于中性原子系综的快速退相干，最高分辨率的激光光谱学通常仅限于单囚禁离子系统。在这里，精密光谱的超冷中性原子限制在一个陷阱的潜力，显示优越的光学相干性，没有任何有害的影响，从运动的自由度，揭示了光学共振线宽在赫兹级具有良好的信噪比。共振品质因数为2.4 x 10^{14}，是任何形式的相干光谱学中恢复的最高值。光谱分辨率允许直接观察到在小磁偏置场下87 Sr的1 S 0和3 P0光学钟态的核自旋简并的破坏。这种类似光学NMR的方法允许精确测量两种状态之间的差分Lande g因子。大量原子的集体激发所表现出的光学原子相干性将对量子测量和精密频率计量产生强烈的影响。
We present a scheme that uses Ramsey interferometry to directly probe the Wigner function of a neutral atom confined in an optical trap. The proposed scheme relies on the well-established fact that the Wigner function at a given point $(x,p)$ in phase space is proportional to the expectation value of the parity operator relative to that point. In this work, we show that parity-even and parity-odd motional states can be mapped to two distinct internal states of the atom by using state-dependent trapping potentials. The Wigner function can thus be measured point-by-point in phase space with a si…
The motion-induced dephasing is a severe problem that limits the accuracy of a quantum control process by using external laser fields in neutral Rydberg atoms. This dephasing is a major issue that limits the realizable fidelity of a quantum entangling gate with neutral atoms when there is a {\it gap} time for the Rydberg atom to drift freely. We find that such a dephasing can be largely suppressed by using a transition in a `V'-type dual-rail configuration. The left~(right) arm of this `V' represents a transition to a Rydberg state $|r_{1(2)}\rangle$ with a Rabi frequency $Ωe^{ikz}~(Ωe^{-ikz})…
Lazy-Move Compilation for Neutral-Atom Quantum Computers via a Buffer-Relay Fabric
Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；Department of Computer Science and Engineering, The Chinese University of Hong Kong（香港中文大学计算机科学与工程系）；Open Quantum Intelligence (Shanghai) Co., Ltd.（上海开放量子智能有限公司）；State Key Laboratory of Quantum Information Technologies and Materials, The Chinese University of Hong Kong（香港中文大学量子信息技术与材料国家重点实验室）；CAS Cold Atom Technology (Wuhan) Co., Ltd.（中科院冷原子技术（武汉）有限公司）；Key Laboratory of Quantum Optics and Center of Cold Atom Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences（中国科学院上海光学精密机械研究所量子光学重点实验室和冷原子物理中心）；State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University（清华大学物理系低维量子物理国家重点实验室）
Laser-cooled atoms coupled to nanophotonic structures constitute a powerful research platform for the exploration of new regimes of light-matter interaction. While the initialization of the atomic internal degrees of freedom in these systems has been achieved, a full preparation of the atomic quantum state also requires controlling the center of mass motion of the atoms at the quantum level. Obtaining such control is not straightforward, due to the close vicinity of the atoms to the photonic system that is at ambient temperature. Here, we demonstrate cooling of individual neutral Cesium atoms,…
High-fidelity collisional quantum gates with fermionic atoms
Max-Planck-Institut für Quantenoptik（马克斯·普朗克量子光学研究所）；Munich Center for Quantum Science and Technology（慕尼黑量子科学与技术中心）；Department of Physics and SUPA, University of Strathclyde（斯特拉斯克莱德大学物理系和SUPA）；Laboratoire Charles Fabry, Institut d’Optique Graduate School, CNRS, Université Paris-Saclay（夏尔·法布里实验室，高等光学学院，法国国家科学研究中心，巴黎萨克雷大学）
Deep Reinforcement Learning for Individual Atomic Control and Cooling
MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics, Massachusetts Institute of Technology（麻省理工学院-哈佛超冷原子中心及电子学研究实验室，麻省理工学院）；Department of Physics, Massachusetts Institute of Technology（麻省理工学院物理系）；Quantum Machines（量子机器）
Scalable quantum computing is based on realizable accurate quantum gates. For neutral atoms, it is an outstanding challenge to design a high-fidelity two-qubit entangling gate without resorting to difficult techniques like shaping laser pulses or cooling atoms to motional ground states. By using spin echo to suppress the blockade error, we propose an easily realizable controlled-phase Rydberg quantum gate of high intrinsic fidelity. In the context of spin echo, we show that the fundamental blockade error of the traditional Rydberg gate, on the order of $ε\sim10^{-3}$, actually results from two…
We introduce and demonstrate a scheme for eliminating the inhomogeneous dephasing of a collective quantum state. The scheme employs off-resonant fields that continuously dress the collective state with an auxiliary sensor state, which has an enhanced and opposite sensitivity to the same source of inhomogeneity. We derive the optimal conditions under which the dressed state is fully protected from dephasing, when using either one or two dressing fields. The latter provides better protection, circumvents qubit phase rotation, and suppresses the sensitivity to drive noise. We further derive expre…
The generation of long-lived entanglement on an optical clock transition is a key requirement to unlocking the promise of quantum metrology. Arrays of neutral atoms constitute a capable quantum platform for accessing such physics, where Rydberg-based interactions may generate entanglement between individually controlled and resolved atoms. To this end, we leverage the programmable state preparation afforded by optical tweezers along with the efficient strong confinement of a 3d optical lattice to prepare an ensemble of strontium atom pairs in their motional ground state. We engineer global sin…
