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 Hall-superconductor 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 time-reversal 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 fault-tolerant 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 2-dimensional 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, point-like topological excitations, and sub-extensive topological degeneracy. By coupling 2d toric code layers and double semion models, we are able to realize the recently proposed X-cube model and a semionic version of it. By coupling X-cube 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 lower-dimernsional states. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R35.00004: Strongly nonlinear displacement measurement in a nano-optomechanical resonator Juha Muhonen, Rick Leijssen, Giada la Gala, Lars Freisem, Ewold Verhagen Creation of non-classical states of mechanical motion is a long-standing goal of experimental physics. One promising approach to achieve this is measurement-based 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 non-classical states, one needs to move away from linear continuous displacement measurements towards non-linear ($x^2$) and possibly also non-continuous (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 single-photon 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 non-linear measurements, as well as the possibilities for pulsed, backaction-evading, measurements. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R35.00005: Optimization schemes for reduction of many-body terms for quantum computations with fermions Panagiotis Kl. Barkoutsos, Nikolaj Moll, Peter W.J. Staar, Andreas Fuhrer, Stefan Filipp, Matthias Troyer, Ivano Tavernelli Many-body fermionic quantum calculations performed on an analog quantum computer suffer from the existence of k-local terms, which represent interactions among more than two qubits. These originate from the application of Jordan-Wigner transformation for fermion-to-qubit 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 k-local terms into a linear combination of 2-local 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 Multi-qubit Quantum Gates with Trapped Ions by Control of the Driving Field Pak Hong Leung The loss of coherence during the implementation of multi-qubit gates has posed a major challenge to fault-tolerant 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 state-dependent 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 modulation-doped 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 cm-3 (critically doped) to 6.0E18 cm-3 (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: High-speed polarization-encoded 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 polarization-encoded quantum key distribution (QKD) transmitter near a 1550-nm wavelength implemented on a CMOS-compatible silicon-on-insulator photonics platform. The transmitter generates arbitrary polarization qubits at gigahertz bandwidth with an extinction ratio better than 30 dB using high-speed carrier-depletion 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 high-speed quantum-secure communications. [Preview Abstract] |
(Author Not Attending)
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R35.00010: Amplified opto-mechanical transduction of virtual radiation pressure Neill Lambert, Mauro Cirio, Kamanasish Debnath, Franco Nori Nano-mechanical 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 opto-mechanical transduction. In this work we study how an opto-mechanical probe can be used to observe virtual photons dressing the quantum ground state of an ultra-strongly coupled light-matter system. We show that such a signature is amplified when the opto-mechanical coupling strength is modulated at the mechanical frequency. Using a low-energy 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 4-potential (producing the same electromagnetic field (EMF) as the standard real 4-potential), 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., 17-26 (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 Anne-Laurence Phaneuf-L'Heureux, Philippe St-Jean, 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 nitrogen-vacancy 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 pseudo-donor 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 spin-photon interfaces. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R35.00013: A single-electron interferometer in silicon Anasua Chatterjee, Sylvain Barraud, Ruben Otxoa, Franco Nori, Sergey Shevchenko, John J L Morton, M Fernando Gonzalez-Zalba Landau-Zener-Stueckelberg (LZS) interferometry has gained prominence as a tool to study the coherent properties and energy level spectrum of quantum systems. Here we present a multi-level LZS interferometry study performed in a silicon-transistor-based 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 non-demolition regime by measuring the dispersive response of a high-frequency 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 even-parity 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 single-electron analogues to optical interferometry. [Preview Abstract] |
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