Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F34: Trapped Ion and Cold Atom Qubits IIFocus Recordings Available

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Sponsoring Units: DQI DAMOP Chair: Natalie Brown, Quantinuum Room: McCormick Place W193A 
Tuesday, March 15, 2022 8:00AM  8:36AM 
F34.00001: 2D Ion Qubit Arrays for Quantum Information Processing Invited Speaker: Philip Richerme The computational difficulty of solving fully quantum manybody spin problems is a significant obstacle to understanding central questions in quantum condensedmatter physics. This talk will introduce how arrays of trapped ions can be engineered and reprogrammed to emulate the behavior of interesting quantum materials. First, I will review some of the groundbreaking experiments exploring the physics of interacting spin systems using 1D chains of ions. Then, I will describe our creation of 2D trappedion arrays using up to 29 ions, which significantly expands the classes of quantum matter that can be emulated. We characterize the lattice site positions, structural phase boundaries, and vibrational mode frequencies of ions in this geometry, as well as heating effects arising from the rf trapping voltage. We conclude that these 2D crystals will serve as a robust platform for quantum simulations of stronglycorrelated matter, and offer several examples of future experiments enabled by this ion geometry. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F34.00002: Exploring a quantuminformationrelevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]_{x} Huma Yusuf, Michael Chilcote, Denis R Candido, Seth Kurfman, Donley S Cormode, Yu Lu, Michael E Flatté, Ezekiel W JohnstonHalperin Here we present a detailed and systematic study of the lowtemperature magnetic resonance properties of the moleculebased ferrimagnet vanadium tetracyanoethylene (V[TCNE]x). We observe resonance linewidths at 5 K consistent with a quality factor of 8,200, comparable to roomtemperature values. This is consistent with scattering from twolevel fluctuators (TLFs), and is expected to lead to further narrowing at temperatures in the milliKelvin range due to freezeout of thermal magnons. These results are notable because they position V[TCNE]x as a viable candidate, competitive with YIG, for lowtemperature microwave applications in quantum information science and technology. The viability of V[TCNE]x as a quantuminformationrelevant material is also enhanced by the ease of deposition and patterned fabrication afforded by our roomtemperature chemical vapor deposition (CVD) system, which allows for facile and versatile onchip integration of V[TCNE]x with prepatterned microwave circuits. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F34.00003: Mitigating Experimental Imperfections with FrequencyModulated Pulses for HighFidelity TwoQubit Gates in Ion Chains Mingyu Kang, Ye Wang, Omid Khosravani, Bichen Zhang, Chao Fang, Qiyao Liang, Shilin Huang, Jungsang Kim, Kenneth R Brown Highfidelity twoqubit gates are essential in many quantum information processing tasks. In a trappedion quantum computer, collective motional modes of the ion chain are used to entangle the internal states of two ions. The quality of the gates suffers when the experimental parameters such as trap frequency and laser intensity differ from the ideal case or fluctuate over time. Here we present two methods of improving the fidelity of frequencymodulated MølmerSørensen gates under experimental imperfections. First, we achieve robustness to motional mode frequency offsets by optimizing average performance over a range of systematic errors using batch optimization. Next, we mitigate dephasing of the motional modes under a known noise spectrum by designing the filter function of the pulse. We present theoretical methods and experimental results [Kang, M. et al., Phys. Rev. Applied 16, 024039 (2021)]. 
Tuesday, March 15, 2022 9:00AM  9:12AM 
F34.00004: Motional Squeezing of a 2D Ion Crystal via Parametric Amplification Matthew J Affolter, Jennifer F Lilieholm, Bryce B Bullock, Allison L Carter, John J Bollinger, Wenchao Ge Improving coherence is a fundamental challenge in quantum simulations and sensing experiments on trapped ions. Here we discuss preliminary experiments attempting to enhance the spinmotion coupling of ions via parametric amplification without a reduction in the spin coherence. These experiments are performed on 2D crystal arrays of over a hundred Be^{+} ions confined in a Penning trap. This device has been used to perform quantum simulations and sense displacements of the ion crystal that are small compared to the ground state zeropoint fluctuations. By oscillating the trapping potential at close to twice the centerofmass mode frequency, we can squeeze the motional mode, which will enhance the spinmotion coupling while maintaining the spin coherence. This will enable higher fidelity simulations and improve our sensitivity to small displacements. 
Tuesday, March 15, 2022 9:12AM  9:24AM 
F34.00005: An Integrated BellState Analyzer on a Thin Film Lithium Niobate Platform Uday Saha, Edo Waks Trapped ions are excellent candidates for quantum computing and quantum networks because of their long coherence times, ability to generate entangled photons as well as high fidelity single and twoqubit gates. To scale up trappedion quantum computing, we need to develop a Bellstate analyzer on a reconfigurable platform that can herald high fidelity entanglement between remote ions. Thinfilm lithium niobate is an attractive platform for its large transparency window and high electrooptic coefficient. However, trapped ions naturally emit polarizationencoded photonic qubits, while thinfilm lithium niobate devices are polarizationsensitive due to the large mode anisotropy created during fabrication. In this work, we design a photonic Bellstate analyzer on a thin film lithium niobate platform for polarizationencoded qubits. We optimize the dimensions of the bell state analyzer and input coupler to achieve polarizationinsensitive operation. We achieve high fidelity entanglement between two trapped ions and determine > 99.99% fidelity in the final optimized device. The proposed Bellstate analyzer can scale up trapped ion quantum computing as well as other optically active spin qubits, such as color centers in diamond, quantum dots, and rareearth ions. 
Tuesday, March 15, 2022 9:24AM  9:36AM 
F34.00006: Deterministic generation of multidimensional photonic cluster states using timedelay feedback Yu Shi, Edo Waks This work proposes a protocol to deterministically generate multidimensional photonic cluster states using a single atomcavity system and timedelay feedback. The dimensionality of the cluster state increases linearly with the number of timedelay feedback. We also give a diagrammatic derivation of the tensor network states, which is valuable in simulating matrix product states and projected entangled pair states generated from sequential photons. Our method provides a simple way to bridge and analyze the experimental imperfections and the logical errors of the generated states. In this method, we analyze the generated cluster states under realistic experimental conditions and address both onequbit and twoqubit errors. 
Tuesday, March 15, 2022 9:36AM  9:48AM 
F34.00007: Enabling SinglePhoton Nonlinear Optics with XPM Temporal Trapping Ryan Hamerly, Ryotatsu Yanagimoto, Edwin Ng, Hideo Mabuchi, Dirk Englund Cavity nonlinear optics (NLO) is an exciting platform for roomtemperature quantum computing, buoyed by recent advances in lowloss dispersionengineered LiNbO_{3} fabrication. Quantum (singlephoton) NLO generally requires operation in the pulsed regime in order to simultaneously leverage the high Q factors of ring resonators and the small effective mode volumes of femtosecond pulses. However, achieving quantum gates in the pulsed regime is complicated by the multimode nature the system, where cavity dispersion and nonlinearity lead to pulse shape distortion and effective qubit decoherence. We propose a temporaltrapping technique based on crossphase modulation (XPM) that projects this complex multimode dynamics down to a single mode set, eliminating the effects of mode distortion. Motivated by optical solitons, XPM trapping works by injecting a classical "trapping" pulse to the cavity and using the XPM phase to induce a timedependent cavity phase shift, leading to temporal confinement to a discrete mode set even in the presence of cavity dispersion. We analyze XPM trapping using matrixproduct state and full quantum simulations, highlight the limitations of the approach, and discuss the prospects for nearterm implementation in a thinfilm LiNbO_{3} platform. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F34.00008: BosonSampling in the collisiondominated regime Salini Karuvade, Barry C Sanders, David L Feder BosonSampling is the computational problem of sampling from the output distribution of a linearoptical interferometer with n singlephoton inputs and m output modes. The interferometer is designed to effect a Haarrandom unitary transformation. BosonSampling is hard to solve classically for m much larger than n unless the polynomial hierarchy collapses to the third level, assuming highly plausible complexitytheoretic conjectures. Yet, even in the collisiondominated regime where m∼n, the case we consider in this work, the bestknown classical algorithm has averagecase time complexity exponential with respect to n. Using a combination of numerical and analytical methods, we analyze the joint photonnumber distribution at the output of the interferometer effecting a Haarrandom unitary transformation. Our results are compared against the special cases of interferometer outputs, such as the uniform distribution over all possible output states as well as output distribution that exhibit Bose enhancement. 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F34.00009: Deterministic TimeBin Entanglement between a Single Photon and an Atomic Ensemble Yong Yu, PengFei Sun, ZiYe An, Jun Li, ChaoWei Yang, XiaoHui Bao, JianWei Pan Hybrid matterphoton entanglement is the building block for quantum networks. It is very favorable if the entanglement can be prepared with a high probability. Here, we report the deterministic creation of entanglement between an atomic ensemble and a single photon by harnessing the Rydberg blockade. We design a scheme that creates entanglement between a single photon's temporal modes and the Rydberg levels that host a collective excitation, using a process of cyclical retrieving and patching. The hybrid entanglement is tested via retrieving the atomic excitation as a second photon and performing correlation measurements, which suggest an entanglement fidelity of 87.8%. Our source of matterphoton entanglement will enable the entangling of remote quantum memories with much higher efficiency. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F34.00010: Storing vectorvortex states of light in an intraatomic frequencycomb quantum memory Chanchal ., G.P. Teja, Christoph Simon, Sandeep K Goyal Photons are a prominent candidate for longdistance quantum communication and quantum information processing. Certain quantum information processing tasks require storage and faithful retrieval of single photons, preserving the internal states of the photons. Here we propose a method to store orbital angular momentum and polarization states of light which facilitates the storage of the vectorvortex states in the intraatomic frequencycombbased quantum memory. We show that an atomic ensemble with two intraatomic frequency combs corresponding to △m = ±1 transitions of similar frequency is sufficient for a robust and efficient quantum memory for vectorvortex states of light. As an example, we show that Cs and Rb atoms are good candidates for storing these internal modes of light. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F34.00011: Realtime capable CCDbased individual trappedion qubit measurement Timko Dubielzig, Sebastian Halama, Niklas Orlowski, Celeste Torkzaban, Christian Ospelkaus We report on the successfull implementation of individual realtime detection of 9Be+ qubit states undergoing coherent excitation using an EMCCD camera. The ions are trapped in a cryogenic surfaceelectrode ion trap with integrated microwave conductors [1] for nearfield quantum control. This kind of trap promises good scalability to a higher number of qubits [2]. Together with the individual realtime detection this is a key requirement for manybody quantum simulation and also errorcorrection protocols in quantum information processing. We discuss known error sources during state preparation and measurement in the order of 0.5 % and comment on the sources and the amount of crosstalk in our detection system. We briefly present the used imaging system and compare the qubit state detection performance of the EMCCD camera with a PMT. 
Tuesday, March 15, 2022 10:36AM  10:48AM 
F34.00012: Towards a faulttolerant universal set of microwave driven quantum gates with trapped ions Ludwig Krinner, Nicolas Pulido, Markus Duwe, Hardik Mendpara, Amado BautistaSalvador, Giorgio Zarantonello, Christian Ospelkaus Quantum computing will eventually require a complete set of quantum gates, with a sufficiently low gateerrorsrate to allow fault tolerance [1]. We implement single and twoqubit gates using microwavegradients [2] as a scalable alternative to the more widely spread optical addressing techniques, which are typically limited by photon scattering. The oscillating gradients are generated by embedded conductors inside the trap structure. We obtain a preliminary infidelity of <10−3 for singlequbit gates and approaching 10−3 for twoqubit operations using this fully integrated approach. The twoqubit gates are shown to be robust with respect to motional quantum bus noise, due to a tailored amplitude modulation protocol [3]. 
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