Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S34: Focus Session: AMO Quantum Information Processing: Photons and Atoms 
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Sponsoring Units: GQI DAMOP Chair: Grant Biedermann, Sandia National Laboratories Room: 704 
Thursday, March 6, 2014 8:00AM  8:36AM 
S34.00001: Classical Computers Very Likely Can Not Efficiently Simulate Multimode Linear Optical Interferometers with Arbitrary FockState InputsAn Elementary Argument Invited Speaker: Jonathan Dowling Aaronson and Arkhipov recently used computational complexity theory to argue that classical computers very likely cannot efficiently simulate linear, multimode, quantum optical interferometers with arbitrary Fock state inputs [S. Aaronson and A. Arkhipov, arXiv:1011.3245]. Here we present an elementary argument that utilizes only techniques from quantum optics. We explicitly construct the Hilbert space for such an interferometer and show that that its dimension scales exponentially with all the physical resources. We then link the simulation of the device to the computationally hard problem of computing the permanent of a matrix. [Preview Abstract] 
Thursday, March 6, 2014 8:36AM  8:48AM 
S34.00002: Efficient separation of the orbital angular momentum eigenstates of light Mehul Malik, Mohammad Mirhosseini, Zhimin Shi, Robert Boyd The orbital angular momentum (OAM) modes of light show great promise as a means to extend quantum communication and computation into the highdimensional regime. OAM modes reside in a discrete, unbounded state space and have the potential to dramatically increase the information capacity of QKD systems. Furthermore, the use a large alphabet increases the tolerance of a QKD system to eavesdropping attacks. A key capability for the use of OAM modes in communication is the ability to efficiently sort single photons based on their OAM content. Here we show an experimental technique that uses two optical transformations in order to do this. The first transformation, demonstrated by Berkhout et al. in 2010, employs a Cartesian to Logpolar transformation to map the azimuthal phase profile of an OAM mode to a tilted planar wavefront, whose tilt is proportional to the OAM quantum number. The second transformation creates seven adjacent copies of the transformed planewave mode, resulting in a mode with a larger size as well as a larger phase ramp. The transformed modes are then focused by a lens to spots with greater than 92\% separation efficiency (97\% in theory). We use a similar technique to sort modes in the angular basis, which is mutually unbiased with respect to the OAM basis. [Preview Abstract] 
Thursday, March 6, 2014 8:48AM  9:00AM 
S34.00003: Measurement and comparisonbased sizes of Schr\"{o}dinger cat states of light Tyler Volkoff We extend several measurementbased definitions of effective ``catsize" to coherent state superpositions with branches composed of either single coherent states or tensor products of coherent states. These effective catsize measures depend on determining the maximal quantum distinguishability of certain states associated with the superposition state: e.g., in one measure, the maximal distinguishability of the branches of the superposition is considered as in quantum binary decision theory; in another measure, the maximal distinguishability of the initial superposition and its image after a oneparameter evolution generated by a local Hermitian operator is of interest. The catsize scaling with the number of modes and mode intensity (i.e., photon number) is compared to the scaling derived directly from the Wigner function of the superposition and to that estimated experimentally from decoherence. We also apply earlier comparisonbased methods for determining macroscopic superposition size that require a reference GHZ state. The case of a hierarchical Schr\"{o}dinger cat state with branches composed of smaller superpositions is also analyzed from a measurementbased perspective. [Preview Abstract] 

S34.00004: ABSTRACT WITHDRAWN 
Thursday, March 6, 2014 9:12AM  9:24AM 
S34.00005: Method for Sorting Photon Orbital Angular Momentum States by Pattern Decomposition Jennifer Lumbres, David Van Buren, Susan Terebey In addition to the photon spin responsible for the two polarization states, photons possess an orbital angular momentum (OAM) with values that are signed integer multiples of hbar and travel in a helical shape. We present a tabletop spectroscopy experiment to generate, manipulate, and measure OAM states of photons from a laser. We create multiple beams with different OAM content using computer generated fork holograms implemented in 35mm film slides. After overlapping the beams into one combined beam, we use multipoint interferometer apertures to interrogate this beam and generate interference patterns on an imaging detector. Since the different OAM states are orthogonal, these patterns sum. A decomposition of the summed pattern is performed using a simple sorting algorithm which retrieves the intensities of each of the original OAM beams. We show several examples of OAM content retrieval via our method.~ This research seeks to perform OAM spectroscopy of natural light sources such as direct and scattered sunlight. [Preview Abstract] 
Thursday, March 6, 2014 9:24AM  9:36AM 
S34.00006: Storing singlephotons in microcavities arrays Imran M. Mirza, S.J. van Enk, H.J. Kimble Coupling light to arrays of microcavities is one of the most promising avenues to store/delay classical light pulses [F. Krauss, Nat. Phot. 2, 448450 (2008)]. However, from the perspective of benefiting quantum communication protocols, the same ideas in principle can be extended down to the singlephoton (quantum) level as well. Particularly, for the purposes of entanglement purification and quantum repeaters a reliable storage of single photons is needed. We consider in our work [I. M. Mirza, S. Van Enk, H. Kimble JOSA B, 30,10 (2013)] cavities that are coupled through an optical fiber which is assumed to be forming a Markovian bath. For this study two powerful open quantum system techniques, InputOutput theory for cascaded quantum systems and the Quantum Trajectory approach are used in combination. For the confirmation of photon delays the TimeDependent Spectrum of such a single photon is obtained. Interestingly this leads to a holeburning effect showing that only certain frequency components in the single photon wavepackets are stored inside the cavities and hence are delayed in time. Since ondemand production of single photons is not an easy task we include in our description the actual generation of the single photon by assuming a single emitter in one the resonators. [Preview Abstract] 
Thursday, March 6, 2014 9:36AM  9:48AM 
S34.00007: Quantum teleportation in artificial photosystems: possibilities and limitations Mehdi Zarea, Raanan Carmieli, Mark Ratner, Michael Wasielewski The possibility of performing quantum teleportation (QT) in a molecular system consisting of an unknown radical spin and a singletcoupled acceptordonor pair is studied. The recombination of radicalacceptor pair to its ground state is spinselective. Here we show that in the presence of exchange interaction between the acceptor and donor, the spinselective recombination acts as the Bell state measurement. The spinrecombination and the exchange interaction derive the initial quantum state to one of the four Bell states; as a result the spin state of the radical is teleported to the donor spin. [Preview Abstract] 
Thursday, March 6, 2014 9:48AM  10:24AM 
S34.00008: Robust and Addressable Control of Atomic Qubits and Qudits Invited Speaker: Poul Jessen The standard paradigm for quantum computation and simulation with neutral atoms assumes that constituent atoms can be used as individually addressable qubits. To accomplish this in optical lattices with submicron atom separation, we have developed a resonance addressing scheme that combines a position dependent light shift of the qubit transition with resonant microwave ($\mu $w) pulses. In a proofofprinciple experiment, we show that numerically optimized composite pulses can implement quantum gates on Cs qubits at targeted lattice sites, with minimal crosstalk to neighboring sites and significant robustness against uncertainty in the atom position. Coherence is verified through twopulse experiments, and the average gate fidelity is measured to be 95$+$/3{\%} [1]. Because most atoms have more than two accessible levels, one might also consider if the existing toolbox for qubit control can be extended to $d$level systems (qudits). Over the past several years we have used the 16dimensional ground hyperfine manifold of cold, untrapped Cs atoms as an experimental testbed for such work. Driving the atoms with a combination of phase modulated radio frequency (rf) and $\mu $w magnetic fields, we use numerical optimization techniques to design control waveforms (rf and $\mu $w phases as function of time) that accomplish a wide range of control tasks, from quantum statetostate maps [2] to full unitary transformations, with average fidelities that vary from \textgreater 99{\%} for the former to $\sim$ 98{\%} for the latter. We further show that tools for inhomogeneous control and dynamical decoupling can be generalized to qudits, allowing transformations that are robust to static as well as dynamic perturbations, and thus in principle compatible with optical traps and the resonance addressing scheme demonstrated for qubits. \\[4pt] [1] J. H. Lee et al., Nature Comm. \textbf{4}, Article no. 2027 (2013), doi:10.1038/ncomms3027.\\[0pt] [2] A. Smith et al, Phys. Rev. Lett. \textbf{111}, 170502 (2013). [Preview Abstract] 
Thursday, March 6, 2014 10:24AM  10:36AM 
S34.00009: Generation of highfidelity spin entanglement by controlling Wannier orbitals of ultracold atoms in an optical lattice Yuuki Tokunaga, Kensuke Inaba, Kiyoshi Tamaki, Kazuhiro Igeta, Makoto Yamashita We propose a method for generating highfidelity multipartite spin entanglement of ultracold atoms in an optical lattice within short operation time, which is suitable for measurementbased quantum computation. To produce the desired spin entanglement, we propose to actively utilize the extra degrees of freedom (DOFs) included in the Hubbard Hamiltonian of atoms, such as, (pseudo)charge and orbital DOFs, which are usually neglected in the perturbative spin interaction. Our active control of the Wannier orbital DOF allows us to overcome the fundamental difficulty of simultaneous achievement of high fidelity, short operation time, and scalability due to the fact that enhancing interaction for short operation time breaks the perturbative condition and intrinsically induces unwanted correlations among spin and the extra DOFs. [Preview Abstract] 
Thursday, March 6, 2014 10:36AM  10:48AM 
S34.00010: Quantum Information with Rydberg atoms: Role of dissipation and decoherence Durga Bhaktavatsala Rao Dasari, Klaus Molmer Originally inhomegeneities, decoherence and decay of the atomic systems were minimized in quantum computing proposals so that their effects would not disturb the ideal unitary evolution of the system. Recent works, however, suggest a quite opposite strategy, where inhomegeneities are created on purpose and and the system is driven on resonance with short lived states such that it dephases and decays to robust steady states. By suitable use of the interactions, these states can be selected, e.g., as entangled states or states encoding the outcome of a quantum computation. We investigate the coherent effects induced by dissipation and decoherence in neutral atom based quantum computing proposals, for creating robust entangled states and long distance gates. We also show that these incoherent effects can also be helpful for deterministic loading of optical traps with single atoms and to reliably store and emit single photons. [Preview Abstract] 
Thursday, March 6, 2014 10:48AM  11:00AM 
S34.00011: Maximally entangled states in a BoseHubbard trimer Sebastian Reyes, Luis MoralesMolina, Miguel Orszag We study the generation of entanglement for interacting cold atoms in a threesite BoseHubbard ring. We propose a scheme by which maximally entangled states (MES) between two distinct atomic species can be prepared. Depending on the choice of experimental parameters, we demonstrate that it is possible to obtain different types of MES. Furthermore, we show that these MES are highly protected against experimental noise, making them good candidates for potential applications. [Preview Abstract] 
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