Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J01: Quantum Computing, Communication, and Information in AMO Systems |
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Sponsoring Units: DAMOP Chair: Ruichao Ma, Purdue Univ Room: 103 |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J01.00001: Robust and high-fidelity quantum entangling gate with neutral Rydberg atoms Xiao-Feng Shi In this talk, I will show some theoretical proposals of quantum entangling gate with neutral Rydberg atoms that have high intrinsic fidelity and are robust against dephasing from the atomic motion. With off-resonant transitions between ground and Rydberg states, it is possible to induce input-state-dependent phase to the two-qubit state, so that entanglement can be created with only one pulse efficiently. This talk also presents schemes for partially suppressing the motional dephasing of the transition between ground and Rydberg states for neutral atoms. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J01.00002: Towards Trapping Electrons in Paul Traps for Quantum Computing Jinen Guo, Clemens Matthiesen, Hartmut Haeffner Trapped-electron qubits provide an interesting alternative to trapped ions in quantum information processing. The operations on trapped electron systems can be all-electronic, making it easier to scale up, and the light mass of electrons enables faster two-qubit gates. In order to evaluate the feasibility of a trapped electron quantum computer, we simulate the electron dynamics inside Paul traps with a drive frequency of 1.5 GHz. From the simulations, we determine the trap depth and explore the validity of pseudopotential approximation. In addition to the electron dynamics in the trapping potential, we also explore how to deterministically eject electrons from the trapping potential towards a particle detector. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J01.00003: Controlling entanglement sudden death in two coupled atoms interacting off-resonance with a radiation field Gehad Sadiek, Wiam Al-Dress We study a system of two coupled two-level atoms (qubits) interacting, at non-zero detuning, with a single mode radiation field. This system is of special interest in the field of quantum information processing (QIP) and can be realized in electron spin states in quantum dots or Rydberg atoms in optical cavities and superconducting qubits in linear resonators. We utilize our exact analytical solution for the time evolution of the system to show how entanglement sudden death (ESD), which represents a major threat to QIP, can be efficiently controlled by tuning atom-atom coupling and non-zero detuning. We demonstrate that while one of these two system parameters may not separately affect the ESD, combining the two can be very effective in reducing, eliminating or creating ESD depending crucially on the system initial state. A synchronization between the population inversion collapse-revival pattern and the entanglement dynamics is observed at all system parameter combinations. The variation of the radiation field intensity shows a clear impact on the duration of the ESD at any combination of the other system parameters. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J01.00004: Realizing the Hayden-Preskill Protocol with Coupled Dicke Models Yanting Cheng, Chang Liu, Jinkang guo, Yu Chen, Pengfei Zhang, Hui Zhai Hayden and Preskill proposed a thought experiment that Bob can recover the information Alice throws into a black hole if he has a quantum computer entangled with the black hole, and Yoshida and Kitaev recently proposed a concrete decoding scheme. Here we propose to realize this decoding protocol in a physical system of two Dicke models, with two cavity fields prepared in a thermofield double state. We show that the Yoshida-Kitaev protocol allows us to read out the initial spin information after it is scrambled into the cavity. We show that the readout efficiency reaches a maximum when the model parameter is tuned to the regime where the system is the most chaotic, characterized by the shortest scrambling time in the out-of-time-ordered correlation function. Our proposal opens up the possibility of discussing this profound thought experiment in a realistic setting. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J01.00005: High-fidelity ground state preparation of single neutral atom in an optical tweezer Xiwang Luo, Mark G Raizen, Chuanwei Zhang Arrays of neutral-atom qubits in optical tweezers are a promising platform for quantum computation. Despite experimental progress, a major roadblock for realizing neutral atom quantum computation is the qubit initialization. Here we propose that supersymmetry---a theoretical framework developed in particle physics---can be used for ultra-high fidelity initialization of neutral-atom qubits. We show that a single atom can be deterministically prepared in the vibrational ground state of an optical tweezer by adiabatically extracting all excited atoms to a supersymmetric auxiliary tweezer with the post-selection measurement of its atomic number. The scheme works for both bosonic and fermionic atom qubits trapped in realistic Gaussian optical tweezers and may pave the way for realizing large scale quantum computation, simulation and information processing with neutral atoms. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J01.00006: A simple embedding scheme for quantum computer simulations of molecules Christina Daniel, Manuel Weber, Dominika Zgid, James Freericks Current era noisy intermediate-scale quantum computers are limited in what they can accurately simulate. One of the most successful applications to date has been the variational quantum eigensolver, which uses the quantum computer to create a trial wavefunction and then employs a simple circuit to measure the expectation value of different pieces of the Hamiltonian. A classical computer is employed to accumulate all of the results and determine the energy; it also is employed to optimize the trial wavefunction, if desired. In this work, we focus on the question of whether one can easily improve the accuracy of this calculation via an embedding strategy. We take a classical Hartree-Fock (or similar) approximation for a large system and correct its energy using the correlation energy derived from the smaller quantum computer calculation. We illustrate this concept with calculations performed on some simple molecules. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J01.00007: Memory-enhanced quantum communication using diamond quantum networks Christian Nguyen, Mihir K Bhaskar, Ralf Riedinger, Bartholomeus J Machielse, David Levonian, Erik Knall, Hongkun Park, Dirk R. Englund, Marko Loncar, Denis D Sukachev, Mikhail Lukin The ability to communicate quantum information over long distances is of central importance in quantum science and engineering. For example, it enables secure quantum key distribution (QKD) relying on fundamental principles that prohibit the "cloning" of unknown quantum states. While QKD is being successfully deployed, its range is currently limited by photon losses and cannot be extended using straightforward measure-and-repeat strategies without compromising its unconditional security. Quantum repeaters, which utilize intermediate quantum memory nodes and error correction techniques, can extend the range of quantum channels. However, their implementation remains an outstanding challenge, requiring a combination of efficient and high-fidelity quantum memories, gate operations, and measurements. Here, we present our approach towards building a quantum repeater using silicon-vacancy color centers (a solid-state quantum memory) integrated into diamond nanophotonic cavities. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J01.00008: Continuous protection of a quantum state from inhomogeneous dephasing Ran Finkelstein, Ohr Lahad, Omri Davidson, Eilon Poem, Ofer Firstenberg Room-temperature atomic vapors are known for their simplicity and their potential scaling-up in applications. In spite of these benefits, laser-cooled atoms have evolved to be the prevalent systems for studying strong and coherent light-matter interactions, as the latter are unhindered by Doppler broadening. Here we present several methods to overcome the effective decrease of both atom-photon cross-section [1] and coherence time in vapors, and in fact in any inhomogeneously broadened atom-like system. The mechanism we study can be understood as the counteraction of the inhomogeneous dephasing of two coupled states, where one state has enhanced sensitivity to the source of dephasing. A far-detuned dressing field admixes a fraction Ω2/△2 of this "sensor" state into the "protected" state, yielding a velocity-insensitive state and line-narrowing in two-color trasnitions [2]. Finally, we apply this method to extend the lifetime of collective excitations stored in a thermal atomic vapor. This method is continuous, in contrast to pulsed echo-based techniques. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J01.00009: Correlation spectroscopy as a tool for comparing optical clocks May Kim, Ethan R. Clements, Kaifeng Cui, Aaron Hankin, Samuel M Brewer, Jwo-Sy Chen, David B Hume, David Leibrandt Highly accurate optical clocks are quantum sensors with fractional frequency uncertainty below one part in 10^18 [1]. Comparisons between such clocks can lead to a better understanding of fundamental physics and potentially replace cesium microwave clocks to redefine the SI second. However, noise from the local oscillator often limits the measurement stability of these comparisons, requiring long averaging times to reduce statistical uncertainty. One way to overcome this limitation is by performing correlation spectroscopy in which a Ramsey pulse sequence derived from the same probe laser is applied to the clocks synchronously. The coherent differential frequency measurements between atomic systems permit interrogation times beyond the laser coherence time, which leads to a reduction in the quantum projection noise limit. As a result, the frequency comparison instability is significantly lower than is possible for incoherent comparisons using the same local oscillator. We demonstrate this technique using two Al+ quantum-logic clocks separated in space by a few meters. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J01.00010: Correlation Spectroscopy Between Two 27Al+ Quantum-Logic Clocks Ethan Clements, May Kim, Kaifeng Cui, Aaron Hankin, Samuel M Brewer, Jwo-Sy Chen, David Leibrandt, David B Hume Correlation spectroscopy is a technique for performing coherent differential frequency measurements between two atomic clocks with an interrogation time beyond the coherence time of the local oscillator. This technique was initially demonstrated for two co-trapped ions [1-3]. Here, we present a demonstration of correlation spectroscopy between two independent 27Al+ optical atomic clocks separated by a few meters. We discuss limitations caused by differential noise sources and techniques that can be used to mitigate these effects. Correlation spectroscopy allows us to extend the interrogation time to 8 seconds, beyond the capability of cavity stabilized lasers and approaching the lifetime limit of the Al+ atomic transition. From this increase in the interrogation time we obtain a fractional measurement instability below 4x10-16 at 1 s, a factor of ~10 improvement from previous Al+ clock comparisons. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J01.00011: Conversion of position correlation into polarization entanglement Chithrabhanu Perumangatt, Alexander Lohrmann, Alexander Ling Photons entangled in polarization have been a prime tool for experiments in fundamental quantum physics. To generate polarization entanglement from spontaneous parametric down conversion (SPDC), it is necessary to impose coherent superposition of two pump-decay paths. There is a variety of techniques by which this coherent superposition can be achieved. Examples of previous entangled photon-pair sources have utilized momentum correlation, indistinguishable pump decay in two separate crystals, or two distinguishable pump beams. We present a method to convert position correlation of photon-pairs into polarization entanglement. This is achieved by individually manipulating the polarization state of photons generated in different parts of a non-linear medium and putting them in coherent superposition. This concept is experimentally demonstrated using photon-pairs produced by SPDC. The method was used to implement a compact source producing an observed photon-pair rate of 120,000/s/mW with an entanglement fidelity of 0.99. This method can be extended to any photon-pair generation process with initial position correlation. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J01.00012: Toward quantum-logic spectroscopy of single molecular ions in a cryogenic ion trap Dalton Chaffee, Alejandra L Collopy, Dietrich Leibfried, David Leibrandt, Chin-wen Chou Quantum state control of trapped and cooled atomic ions is an established technique with applications including precision metrology and quantum computing. Molecules provide even richer physics, but their additional degrees of freedom make such control more challenging. In our group, quantum-logic spectroscopy (QLS) of a single CaH+ ion has enabled preparation and coherent manipulation of pure molecular quantum states [1]. However, the currently used loading scheme is applicable only to certain hydrides, and background gas collisions and black-body radiation in the room-temperature apparatus eventually limit measurement precision and fidelity of quantum control. Here, we present progress of the design and construction of a cryogenic ion trap apparatus for more versatile loading of molecular ions and better control of their states. Molecules will be injected from an interchangeable gas source, ionized in a strong laser field, and co-trapped with an atomic ion for QLS. This device will be used to perform precision spectroscopy of molecules relevant for, e.g., tests of fundamental physics. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J01.00013: Towards quantum logic spectroscopy of multi-ion arrays Kaifeng Cui, Kevin T Boyce, David Leibrandt, David B Hume We describe a new approach for precision spectroscopy of trapped ions using quantum logic. Our approach adapts method developed in the context of quantum information processing to non-destructive detection of the 1S0-3P0 clock transition in 27Al+. A state-dependent force is employed on the spectroscopy ion(s) to modulate the qubit state of the detection ion(s), similar to the techniques employed for high-fidelity quantum gates[1,2] and sensitive force detection experiments [3,4]. This method does not require ground state cooling and would enable scaling to large numbers of spectroscopy ions to improve ion clock stability. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J01.00014: Direct characteristic-function tomography of quantum states of the trapped-ion motional oscillator Christa Flühmann Quantum state reconstruction is an important element enabling diagnosis and improvement of quantum control. As larger states come under experimental control the number of measurements required to perform state reconstruction becomes crucial. Here, significant gains can be found by choosing the appropriate basis in which to make measurements. In this talk I will present recent experiments analyzing direct phase-space tomography of the motion of a single trapped Ca+ ion. The method, which is based on ion internal state rotations combined with state-dependent shifts of the oscillator, is used to reconstruct displaced squeezed oscillator states as well as a three-component superposition thereof. Such states have applications in quantum information, quantum sensing and fundamental studies. We find reductions in measurement times of a factor 20 compared to methods we used previously, which we anticipate to improve future ion motion state preparation and control. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J01.00015: High dimensional entanglement between a photon and a multiplexed atomic quantum memory Chang Li, Yukai Wu, Wei Chang, Sheng Zhang, Luming Duan Multiplexed quantum memories and high-dimensional entanglement can improve the performance of quantum repeaters by promoting the entanglement generation rate and the quantum communication channel capacity. Here, we experimentally generate a high-dimensional entanglement between a photon and a collective spin wave excitation stored in the multiplexed atomic quantum memory. We verify the entanglement dimension by the quantum witness and the entanglement of formation. Then we use the high-dimensional entangled state to test the violation of Bell-type inequality. Our work provides a prominent method to generate multidimensional entanglement between the flying photonic qubits and the atomic quantum interfaces, a key step toward quantum networks. |
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