Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A28: AMO Quantum InformationFocus

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Sponsoring Units: DQI DAMOP Chair: Julian Leonard, ETH Zurich Room: BCEC 161 
Monday, March 4, 2019 8:00AM  8:12AM 
A28.00001: Coherent control of large ion crystals in a Penning trap quantum simulator Christian Marciniak, Robert Wolf, Michael Jordan Biercuk We will present recent achievements towards building a quantum simulator for transversefield Isingtype Hamiltonians based on lasercooled Coulomb crystals of ^{9}Be^{+} in a Penning trap. We introduce the overall system design and describe key technical elements that have permitted siteresolved imaging of rapidly rotating 2D ion crystals with > 70 ions, stable over tens of seconds. Novel approaches to ion imaging using a room temperature APDarraycamera coupled to a microlens array are also presented as a means to achieve highspeed state detection with spatial resolution. In addition, we demonstrate coherent control over the ions’ electron spin using millimeter waves near 55 GHz via a custom highstability source and delivery system. 
Monday, March 4, 2019 8:12AM  8:24AM 
A28.00002: Integrated multiwavelength photonic addressing of trapped ion qubits Robert Niffenegger, Jules Stuart, Colin Bruzewicz, Robert McConnell, Gavin West, Garrett Simon, Dave Kharas, Cheryl SoraceAgaskar, Suraj Bramhavar, Jeremy Sage, John Chiaverini Integrating quantum and classical technologies with systems like trapped ions is critical to enable the Moore’s law like scaling of qubits necessary to develop practical quantum computers. For instance, individual addressing of trapped ion qubits typically requires bulky free space optics to tightly focus multiple laser beams onto single ions within linear chains, limiting scalability. Here we have designed and fabricated an ion trap chip with integrated photonic waveguides and grating outcouplers for integrated addressing in all of the infrared, visible, and ultraviolet wavelengths required to cool and control ^{88}Sr+ trapped ion qubits. The combination of recently developed low loss UV photonic waveguides made from Al_{2}O_{3} with more typical SiN waveguides for IR and visible wavelengths within multiple layers of the chip enables integration of light at all the wavelengths required for ion control. We study the interaction of these new multiwavelength photonics with a single ion qubit towards demonstration of a two qubit gate controlled via integrated technologies, a key component of a scalable trapped ion quantum information processor. 
Monday, March 4, 2019 8:24AM  8:36AM 
A28.00003: Phasemodulated entangling gates robust against static and timevarying errors Alistair Milne, Claire Edmunds, Cornelius Hempel, Virginia Frey, Sandeep Mavadia, Michael Jordan Biercuk In a prominent class of entangling gates, encompassing the MølmerSørensen gate in trapped ions and the resonatorinduced phase gate in superconducting circuits, qubits are entangled via shared coupling to bosonic oscillator modes. A major source of error in these entangling gates is residual qubitoscillator coupling at the conclusion of an operation. We present a technique that employs discrete phase shifts in the mediating field driving the gate to ensure all modes are deexcited at arbitrary userdefined times, increasing the gate fidelity and scalability. We demonstrate its use across a range of parameters with a pair of ^{171}Yb^{+} ions and observe a significant reduction in gate error under nonideal conditions, saturating measurementfidelity limits (~97%) in cases where an unmodulated "primitive" gate would only achieve ~50% fidelity. The technique provides a unified framework to achieve robustness against both static and timevarying error sources captured in the filterfunction formalism. Experiments agree well with theoretical predictions for gate robustness as a function of static detuning and timedependent laser amplitude and trapfrequency error processes. 
Monday, March 4, 2019 8:36AM  8:48AM 
A28.00004: Nonlinear quantum Rabi model in trapped ions Iñigo Arrazola, XiaoHang Cheng, Julen S. Pedernales, Lucas Lamata, Xi Chen, Enrique Solano We study the nonlinear dynamics of trappedion models far away from the LambDicke regime. This nonlinearity induces a blockade on the propagation of quantum information along the Hilbert space of the JaynesCummings and quantum Rabi models. We propose to use this blockade as a resource for the dissipative generation of highnumber Fock states. Also, we compare the linear and nonlinear cases of the quantum Rabi model in the ultrastrong and deep strongcoupling regimes. Moreover, we propose a scheme to simulate the nonlinear quantum Rabi model in all coupling regimes. This can be done via offresonant nonlinear red and bluesideband interactions in a single trapped ion, yielding applications as a dynamical quantum filter. 
Monday, March 4, 2019 8:48AM  9:00AM 
A28.00005: Characterizing Unwanted Motional Coupling in MølmerSørensen Gates Leonardo Andreta de Castro, Pak Hong Leung, Pavithran S Iyer, Kenneth R Brown Mølmer–Sørensen gates constitute an integral hardware component of an ion trap quantum computer. These gates entangle qubits to motional modes of the ions, generating phonons that manifest in errors on future gates. As a result, the analysis of fault tolerant quantum computation schemes becomes challenging. In this work, we quantify the impact of ignoring nonMarkovian features in the noise model for Mølmer–Sørensen gates by developing numerical tools to compute the fidelity of a sequence of N Mølmer–Sørensen gates. Although completely ignoring nonMarkovianity results in an overestimation of this fidelity, we present Markovian models that can reproduce the same scaling of fidelity as the true noise process. These accurate Markovian models rely on a heuristic assumption that the displacements of the motional modes resemble a random walk. 
Monday, March 4, 2019 9:00AM  9:12AM 
A28.00006: Scalable Trapped Ion Architectures and Micromotion Enhancement Alexander Ratcliffe, Joseph Hope Quantum computing promises exciting new opportunities to answer currently intractable problems. To achieve this feat, a quantum architecture that is able to perform high fidelity operations and can be readily scaled to large numbers of qubits is required. The main obstacle to quantum computation being used as another computational tool is the limited scalability of current architectures. Trapped ions are prensently one of the most promising platforms for large scale quantum computing, achieving high fidelity operations and long coherence times. Their current limitation lies in scalability. Most proposals to overcome this require coupling to many small trapped ion systems via an optical bus, or call for ions to be shuttled between segments of the system. Both of these proposals introduce new challenges and increase the complexity of the platform. Here, I demonstrate that a simple approach to scalability using microtrap arrays provides a feasible road to scalability. I show that this can be achieved without introducing any more complexity to the system than is required for trapping. Further, I show that this is realistically achievable with already demonstrated technology. Finally, I show that within this scheme, an old foe —micromotion —becomes an unlikely ally. 
Monday, March 4, 2019 9:12AM  9:24AM 
A28.00007: Onchip optical quantum memory using erbium ions Ioana Craiciu, Mi Lei, Jake Rochman, Jonathan Kindem, John Bartholomew, Evan Miyazono, Tian Zhong, Andrei Faraon Rare earth ion doped crystals provide an excellent solid state platform for optical quantum memories, which will enable long distance quantum communication and modular quantum computing. Among rare earths, erbium is appealing due to its long lived telecom wavelength resonance, allowing integration with silicon and with existing optical communication technology and infrastructure. 
Monday, March 4, 2019 9:24AM  9:36AM 
A28.00008: Probing amplified spontaneous emission to superradiance transition in cold Cs atoms inside a hollowcore photoniccrystal fiber Zhenghao Ding, Tae Hyun Yoon, Jeremy Flannery, Paul Anderson, Brian Duong, ShengXiang Lin, Fereshteh Rajabi, Martin Houde, Rubayet Al Maruf, Michal Bajcsy We investigate the critical conditions to realize the transition from amplified spontaneous emission (ASE) to superradiance (SR) with an ensemble of lasercooled Cs atoms inside a hollowcore photonic crystal fiber (HCPCF). In our experiment, the Cs atoms, initially cooled using a magnetooptical trap (MOT), are guided and confined inside a short piece of HCPCF with a magicwavelength dipole trap. This work constitutes the preliminary elements of our current experimental investigations towards realization of an ultranarrow linewidth superriant laser. Additionally, we aim to study long range coherence in atomic ensembles and explore the symmetries governing atomfield couplings in the HCPCF platform. 
Monday, March 4, 2019 9:36AM  9:48AM 
A28.00009: Time/frequency highdimensional entanglement via engineered parametric down conversion Francesco Graffitti, Peter Barrow, Massimiliano Proietti, Alex Pickston, Dmytro Kundys, Agata M Branczyk, Alessandro Fedrizzi Photonic quantum technologies rely on the deterministic preparation of qubits encoded in singlephotons degrees of freedom (DoF). While polarisation, orbital angular momentum and path have been routinely used since the early days of quantum information, the last few years have seen an increasing interest in the frequencytime encoding, due to the possibility of generating highdimensional states combined with the compatibility of frequency modes with standard optical components. 
Monday, March 4, 2019 9:48AM  10:00AM 
A28.00010: PolarizationIndependent Photon Storage System with Variable Time Delay Michelle Victora, Fedor Bergmann, Michael E Goggin, Jia Jun Wong, Paul G Kwiat Quantum optical memories are a key component to a variety of quantum information applications, from extending quantum communication channels to building highefficiency singlephoton sources to synchronizing multiple protocols. However, most current broad bandwidth photon storage systems operate with somewhat shorter storage times (on the order of 10 ns), or require cryogenic operation. Here we develop a system with multiplexed freespace storage cavities, able to store single photons with high efficiency over variable delays [N x 12.5 ns, 1 ≤ N ≤ 999], and over several nanometers bandwidth. The system can store multiple photons simultaneously and can potentially store qubits encoded in various degrees of freedom, e.g., spatial modes, timebin, and polarization. For the latter, we have demonstrated a memory fidelity >90% for storage times up to 500 ns. A future goal for this experiment is to achieve storage of hyperentanglement. While previous hyperentangled photon storage systems only achieved 5% efficiency, we have currently demonstrated a freespace transmission above 50% for delay times up to 5 μs. 
Monday, March 4, 2019 10:00AM  10:12AM 
A28.00011: Efficient TwoPhoton Interference with PulseDriven Quantum Emitters in Dynamic Environments Herbert Fotso The ability to achieve distributed entanglement across distant quantum nodes is essential for the construction of scalable quantum networks and other fundamental quantum information processing operations including quantum teleportation and Bell inequality tests[1, 2]. For solidstate spin qubits, it can be achieved through photon interference on a beam splitter. The efficiency of these interference operations rely on the indistinguishability of photons arriving from different emitters. However, for quantum emitters in dynamic environments, uncorrelated environment fluctuations lead to differences in temporal and spectral profiles of emitted photons resulting in reduced photon indistinguishability. We simulate the TPI operation in a HongOuMandeltype experiment for two distant qubits in diffusioninducing environments. We find that when the emitters are driven by appropriate pulse sequences, besides their emission spectra having little dependence on the environment[3, 4], photon indistinguishability can be restored to optimal values paving the way for improved efficiency in photonmediated QIP operations. 
Monday, March 4, 2019 10:12AM  10:24AM 
A28.00012: Universal Dynamics of Inhomogeneous Quantum Phase Transitions: Suppressing Defect Formation Fernando GómezRuiz, Adolfo Del Campo In the nonadiabatic dynamics across a quantum phase transition, the KibbleZurek mechanism predicts that the formation of topological defects is suppressed as a universal power law with the quench time. In inhomogeneous systems, the critical point is reached locally and causality reduces the effective system size for defect formation to regions where the velocity of the critical front is slower than the secondsound velocity, favoring adiabatic dynamics. The reduced density of excitations exhibits a much steeper dependence on the quench rate and is also described by a universal powerlaw, that we demonstrated in a quantum Ising chain. 
Monday, March 4, 2019 10:24AM  11:00AM 
A28.00013: Controlling Quantum Spin States and Dynamics with Light Invited Speaker: Monika SchleierSmith Coupling many atoms to a single mode of light provides an efficient means of generating quantum correlations in an extended manybody system. I will report on experiments in which we harness photons in an optical cavity to mediate “flipflop” interactions among distant spins in a millimeterlong cloud of atoms, as we directly observe by imaging quench dynamics. In our spin1 system, these exchange interactions enable correlated pair creation in the m = ±1 Zeeman states, a process analogous to spontaneous parametric downconversion or to collisional spin mixing in BoseEinstein condensates. In contrast to direct collisional interactions, nonlocal lightmediated interactions offer unprecedented opportunities for engineering the spatial structure of spinspin couplings and correlations. I will describe progress and prospects in tailoring atomlight interactions to enable new directions in quantum simulation and to generate new resources for quantumenhanced sensing. 
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