Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R35: New Frontiers in Quantum Information 
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Sponsoring Units: GQI Chair: David DiVincenzo, RWTH Aachen University and Forschungs Zentrum Juelich Room: 298 
Thursday, March 16, 2017 8:00AM  8:12AM 
R35.00001: Topological gapped edge states in fractional quantum Hallsuperconductor heterostructures Ashley Cook, C\'{e}cile Repellin, Nicolas Regnault, Titus Neupert We propose and implement a numerical setup for studying edge states of fractional quantum Hall droplets with a superconducting instability. We focus on a timereversal symmetric bilayer fractional quantum Hall system of Laughlin $\nu=1/3$ states. The fully gapped edges carry a topological parafermionic degree of freedom that can encode quantum information protected against local perturbations. We numerically simulate such a system using exact diagonalization by restricting the calculation to the Laughlin quasihole subspace. We study the quantization of the total charge on each edge and show that the ground states are permuted by spin flux insertion and the parafermionic Josephson effect, evidencing their topological nature and the Cooper pairing of fractionalized quasiparticles. [Preview Abstract] 
Thursday, March 16, 2017 8:12AM  8:24AM 
R35.00002: A neural decoder for topological codes Giacomo Torlai, Roger Melko Topological codes are the leading candidate for a practical implementation of faulttolerant quantum computing hardware. The quantum information is protected through an error correction protocol, which is implemented by a ``decoder''  a classical algorithm running on conventional computers. I will introduce a new decoder for generic degenerate stabilizers codes that exploits modern machine learning techniques. The error correction is performed by a neural network, which has no specialization regarding the noise model, nor does it rely on the code geometry or stabilizer group. I will show the neural decoder's performances for the prototypical example of the 2dimensional toric code. [Preview Abstract] 
Thursday, March 16, 2017 8:24AM  8:36AM 
R35.00003: Fracton topological order via coupled layer construction Han Ma, Ethan Lake, Xie Chen, Michael Hermele In this work, we develop a coupled layer construction of exactly solvable models of fracton topological order. These states are characterized by immobile, pointlike topological excitations, and subextensive topological degeneracy. By coupling 2d toric code layers and double semion models, we are able to realize the recently proposed Xcube model and a semionic version of it. By coupling Xcube models, we propose a new model exhibiting fracton topological order, dubbed the four color cube (FCC) model. The coupling mechanisms can be understood as condensation of strings or membranes built from point particles. This work allows some fracton topological phases to be understood in terms of the degrees of freedom of familiar lowerdimernsional states. [Preview Abstract] 
Thursday, March 16, 2017 8:36AM  8:48AM 
R35.00004: Strongly nonlinear displacement measurement in a nanooptomechanical resonator Juha Muhonen, Rick Leijssen, Giada la Gala, Lars Freisem, Ewold Verhagen Creation of nonclassical states of mechanical motion is a longstanding goal of experimental physics. One promising approach to achieve this is measurementbased state preparation where sufficiently strong interaction with a measurement device is used to project the mechanics into an eigenstate of the measured observable. In order to prepare nonclassical states, one needs to move away from linear continuous displacement measurements towards nonlinear ($x^2$) and possibly also noncontinuous (pulsed) measurements. We present here strongly nonlinear measurement of a mechanical resonator in a novel nanophotonic cavity optomechanical system with a record high optomechanical coupling strength. Although the coupling between displacement and optical cavity frequency is itself linear, the high interaction strength in combination with narrow optical linewidth (resulting in a singlephoton cooperativity $C_0>1000$) allows us to use the second order working point of a homodyne interferometer to perform a sensitive $x^2$ measurement, with noise floor at $\sim 100$ $x_{zpf}^2/\sqrt{Hz}$. We discuss future potential to reach the quantum regime with such nonlinear measurements, as well as the possibilities for pulsed, backactionevading, measurements. [Preview Abstract] 
Thursday, March 16, 2017 8:48AM  9:00AM 
R35.00005: Optimization schemes for reduction of manybody terms for quantum computations with fermions Panagiotis Kl. Barkoutsos, Nikolaj Moll, Peter W.J. Staar, Andreas Fuhrer, Stefan Filipp, Matthias Troyer, Ivano Tavernelli Manybody fermionic quantum calculations performed on an analog quantum computer suffer from the existence of klocal terms, which represent interactions among more than two qubits. These originate from the application of JordanWigner transformation for fermiontoqubit map, to the electronic Hamiltonians in second quantization form. Existing solutions to this problems rely on the use of perturbation theory via Hamiltonian gadgets. The main obstacle associated to this technique is the introduction of large coupling constants, which are several orders of magnitude larger than the terms in the unperturbed physical Hamiltonian. To improve on it, we propose a new optimization scheme, that unfolds the klocal terms into a linear combination of 2local terms in the enlarged Hilbert space, built as a tensor product between the physical and ancilla space. The optimization procedure ensures that the physical properties of the new Hamiltonian (eigenspectrum and density matrices) remain the same as in the original, while keeping all coupling constants comparable in size, making it better suited for an experimental quantum computer implementation. [Preview Abstract] 
Thursday, March 16, 2017 9:00AM  9:12AM 
R35.00006: Cavity optomechanics with micromirrors: Measuring and reducing radiation pressure noise with bright squeezed light Jonathan Cripe, Robinjeet Singh, Min Jet Yap, Garrett Cole, Thomas Corbitt On September 14, 2015, LIGO made the first direct detection of gravitational waves. Advanced LIGO is predicted to be limited by quantum noise at intermediate and high frequencies when it reaches design sensitivity in the next couple years. The quantum noise, including radiation pressure noise at intermediate frequencies, will need to be reduced in order to increase the sensitivity of future gravitational wave interferometers. We report recent progress towards measuring quantum radiation pressure noise in an optomechanical cavity and the reduction of radiation pressure noise using bright squeezed light. The low noise, microfabricated mechanical oscillator also allows for direct broadband thermal noise measurements which test thermal noise models and damping mechanisms and serves as a test bed for the application of crystalline coatings in future gravitational wave detectors. These techniques may be applicable to an upgrade of Advanced LIGO or the next generation of gravitational wave detectors. [Preview Abstract] 
Thursday, March 16, 2017 9:12AM  9:24AM 
R35.00007: Decoherence Suppression in Multiqubit Quantum Gates with Trapped Ions by Control of the Driving Field Pak Hong Leung The loss of coherence during the implementation of multiqubit gates has posed a major challenge to faulttolerant quantum computation. For example, residual entanglement between the internal and motional states of trapped ions at the end of quantum gates is a key contributor to fidelity loss. It is therefore crucial to minimize the phase space displacement due to statedependent forces upon completion of the gate. We will show that in theory we can suppress the effect of the displacement operator for relevant modes by using an oscillatory laser detuning pattern. This method may be combined with previous efforts on amplitude and phase modulation, leading to more complex parallel gate operations on an ion chain that are robust against heating of motional modes. [Preview Abstract] 
Thursday, March 16, 2017 9:24AM  9:36AM 
R35.00008: Effect of doping density concentration in modulationdoped GaAs/AlGaAs heterostructures on charge noise in quantum point contacts Saeed Fallahi, James Nakamura, Michael Yannell, Michael Manfra Low frequency charge noise is an important consideration for semiconductor spin qubits that may limit coherence times. We present measurements of low frequency charge noise in modulation doped GaAs/AlGaAs heterostructures grown by molecular beam epitaxy in which the silicon doping density has been varied from 2.4E18 cm3 (critically doped) to 6.0E18 cm3 (overdoped) within a fixed thickness.. We have fabricated quantum point contacts (QPCs) on these heterostructures with different QPC widths ranging from 300nm to 500nm. We measured current noise through quantum point contact (QPC) on the riser of the first quantized conductance plateau. These QPCs provide a sensitive probe of charge noise in the heterostructure. We present data demonstrating the relationship between low frequency noise and density and placement of silicon donors. We have also investigated influence of dimeric (As2) vs tetrameric (As4) arsenic vapor species during MBE growth on charge noise and its relation to the formation of electron trapping centers. [Preview Abstract] 
Thursday, March 16, 2017 9:36AM  9:48AM 
R35.00009: Highspeed polarizationencoded quantum key distribution based on silicon photonic integrated devices Darius Bunandar, Junji Urayama, Nicholas Boynton, Nicholas Martinez, Christopher DeRose, Anthony Lentine, Paul Davids, Ryan Camacho, Franco Wong, Dirk Englund We present a compact polarizationencoded quantum key distribution (QKD) transmitter near a 1550nm wavelength implemented on a CMOScompatible silicononinsulator photonics platform. The transmitter generates arbitrary polarization qubits at gigahertz bandwidth with an extinction ratio better than 30 dB using highspeed carrierdepletion phase modulators. We demonstrate the performance of this device by generating secret keys at a rate of 1 Mbps in a complete QKD field test. Our work shows the potential of using advanced photonic integrated circuits to enable highspeed quantumsecure communications. [Preview Abstract] 
(Author Not Attending)

R35.00010: Amplified optomechanical transduction of virtual radiation pressure Neill Lambert, Mauro Cirio, Kamanasish Debnath, Franco Nori Nanomechanical devices are widely used to measure a variety of weak signals: optical, electrical and even gravitational. This is partly due to the versatility of mechanical modes to interact with other systems. For example, radiation pressure, the transfer of momentum from photons to phonons, is the physical principle allowing for optomechanical transduction. In this work we study how an optomechanical probe can be used to observe virtual photons dressing the quantum ground state of an ultrastrongly coupled lightmatter system. We show that such a signature is amplified when the optomechanical coupling strength is modulated at the mechanical frequency. Using a lowenergy approximation we calculate analytically the limit on the thermal noise tolerated by this scheme. [Preview Abstract] 
Thursday, March 16, 2017 10:00AM  10:12AM 
R35.00011: No Drama Quantum Electrodynamics? Andrey Akhmeteli Is it possible to offer a ``no drama'' quantum electrodynamics, as simple (in principle) as classical electrodynamics  a theory described by a system of partial differential equations (PDE) in 3+1 dimensions, but reproducing unitary evolution of a quantum field theory in the Fock space? The following results suggest an affirmative answer: 1. The scalar field can be algebraically eliminated from scalar electrodynamics. 2. After introduction of a complex 4potential (producing the same electromagnetic field (EMF) as the standard real 4potential), the spinor field can be algebraically eliminated from spinor electrodynamics. 3. The resulting theories describe independent evolution of EMF and can be embedded into quantum field theories. Another fundamental result: in a general case, the Dirac equation is equivalent to a 4th order PDE for just one component, which can be made real by a gauge transform. Issues related to the Bell theorem are discussed. A. Akhmeteli, Int'l Journal of Quantum Information, Vol. 9, Suppl., 1726 (2011) A. Akhmeteli, Journal of Mathematical Physics, Vol. 52, 082303 (2011) A. Akhmeteli, arXiv:1111.4630 A. Akhmeteli, European Physical Journal C, Vol. 73, 2371 (2013) (open access)A. Akhmeteli, arXiv:1502.02351 [Preview Abstract] 
Thursday, March 16, 2017 10:12AM  10:24AM 
R35.00012: Radiative lifetime of excitons and trions bound to Te isoelectronic centers in ZnSe AnneLaurence PhaneufL'Heureux, Philippe StJean, Sebastien Francoeur Atomic defects are interesting candidates for the realization of exciton and spin qubits. Isoelectronic centers in semiconductor materials are particularly appealing as they combine the narrow linewidth transitions and homogeneity of quantum defects like nitrogenvacancy centers in diamond with the high dipole moments of large nanostructures like quantum dots. In this work, we study the emission from pairs of tellurium atoms in ZnSe. This pseudodonor isoelectronic center can bind a hole, an exciton, a trion, or a biexciton. We report on the emission lifetime and, through resonant luminescence and Rabi oscillation measurements, we evaluate the dipole moment of excitons and trions, which can be relatively large due to the particular binding mechanism of these complexes to isoelectronic centers. Thus, by providing strong interactions with photons, these semiconductor defects are promising spinphoton interfaces. [Preview Abstract] 
Thursday, March 16, 2017 10:24AM  10:36AM 
R35.00013: A singleelectron interferometer in silicon Anasua Chatterjee, Sylvain Barraud, Ruben Otxoa, Franco Nori, Sergey Shevchenko, John J L Morton, M Fernando GonzalezZalba LandauZenerStueckelberg (LZS) interferometry has gained prominence as a tool to study the coherent properties and energy level spectrum of quantum systems. Here we present a multilevel LZS interferometry study performed in a silicontransistorbased charge qubit, tunnel coupled to a fermionic sea that allows us to characterise the qubit dynamics in the strong driving regime. We read out the charge state of the system in a continuous nondemolition regime by measuring the dispersive response of a highfrequency resonator coupled to the quantum system via the gate. By performing multiple fast passages through the qubit's avoided crossing we observe the emergence of a LZS interferometry pattern. At higher drives, using a projective measurement to an evenparity charge state, we demonstrate a strong geometrical enhancement of the readout signal. At even higher drives, we perform a second projective measurement during the coherent evolution, resulting in a loss of the interference pattern. Our results demonstrate a way to increase the state readout signal of coherent quantum systems and replicate singleelectron analogues to optical interferometry. [Preview Abstract] 
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