Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session T5: Novel Optical Technologies and Quantum Information |
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Chair: Alex Kuzmich, Georgia Institute of Technology Room: A705 |
Friday, June 17, 2011 8:00AM - 8:12AM |
T5.00001: Hiding Single Photons with Spread Spectrum Technology Chih-Sung Chuu, Chinmay Belthangady, Ite Yu, G.Y. Yin, J.M. Kahn, S.E. Harris We describe a proof-of-principal experiment demonstrating the use of spread spectrum technology at the single photon level. We show how single photons with a prescribed temporal shape, in the presence of interfering noise, may be hidden and recovered. [Preview Abstract] |
Friday, June 17, 2011 8:12AM - 8:24AM |
T5.00002: Multi-Client Quantum Key Distribution using Wavelength Division Multiplexing B. Williams, R. Bennink, D. Earl, P. Evans, W. Grice, T. Humble, R. Pooser, J. Schaake Quantum Key Distribution (QKD) exploits the rules of quantum mechanics to generate and securely distribute a random sequence of bits to two spatially separated clients. Typically a QKD system can support only a single pair of clients at a time. We overcome this limitation with the design and characterization of a multi-client entangled-photon QKD system with the capacity for up to 100 clients simultaneously. The telecom-wavelength entangled photon pairs are generated in a broadband down-conversion source configured for time-bin entangled QKD. The photons are strongly correlated in energy and are emitted across a large spectrum. Using standard wavelength division multiplexing hardware, the photons can be routed to different parties on a quantum communication network, while the strong spectral correlations ensure that each client is ``linked'' only to the client receiving the conjugate wavelength. In this way, a single down-conversion source can support dozens of channels simultaneously. [Preview Abstract] |
Friday, June 17, 2011 8:24AM - 8:36AM |
T5.00003: Efficient benchmarking of quantum optical devices via entanglement measures Nathan Killoran, Norbert Lutkenhaus To carry out quantum communication protocols with light, we need quantum-enabled devices which can safely store and transmit quantum information, including quantum channels, repeaters, and memories. These devices must provide an inherent quantum advantage, outperforming all classical devices, even in the presence of imperfections. To be in the quantum domain, a device must preserve the correlations present in entangled states. Many benchmarks have been designed based on this idea. We have developed qualitative benchmarks requiring very limited experimental resources. In fact, we need as little as two test states and two homodyne measurements to find the quantum domain. Here, we extend these benchmarks, for free, to give quantitative statements about how much entanglement a device preserves. Our extension is based on truncating states to a finite energy level and using known measurement results to rigorously bound the induced error. A semidefinite program is employed to find the minimal entanglement compatible with the known information. Our results are faithful to the known benchmarks, providing quantitative statements for devices throughout the quantum domain. [Preview Abstract] |
Friday, June 17, 2011 8:36AM - 8:48AM |
T5.00004: Few-Photon Switching via Two-Photon Absorption in Rb-Filled Photonic Bandgap Fibers Vivek Venkataraman, Kasturi Saha, Pablo Londero, Alexander Gaeta We demonstrate 40{\%} all-optical modulation with 1 nW of total power via non-degenerate two-photon absorption in Rb vapor confined to a hollow-core photonic bandgap fiber. A 780-nm beam tuned to the 5S$_{1/2} \quad \to $ 5P$_{3/2}$ transition of Rb-85 is used to attenuate a counterpropagating 776-nm beam which is tuned to the 5P$_{3/2} \quad \to $ 5D$_{5/2}$ transition. We observe appreciable nonlinear absorption with powers as low as 360 pW and 720 pW in the 776 nm and 780 nm beams, respectively. The Doppler-free, transit-time-limited transmission profile implies that on average only 6 and 12 photons in the 776-nm and 780-nm beams, respectively, interact with the atoms within the inferred 4.5-ns transit time. Such a system offers the potential to explore novel classical and quantum nonlinear effects at ultralow powers such as single-photon all-optical switching, the generation and measurement of non-classical states of light, and higher-order nonlinear susceptibilities. [Preview Abstract] |
Friday, June 17, 2011 8:48AM - 9:00AM |
T5.00005: Study of two-photon deterministic, passive quantum logical gates Julio Gea-Banacloche, Leno Pedrotti We use a ``modes of the universe'' approach to study a cavity-mediated two-photon logical gate recently proposed by Koshino, Ishizaka and Nakamura [Phys. Rev. A 82, 010301(R) (2010)]. This is the first conceptually feasible deterministic and passive (i.e., requiring no external auxiliary fields) two-photon gate enabling universal quantum computation. We show that the gate can work both in the good and bad cavity limits, provided only that the single-photon pulses are long enough. We derive analytical estimates for the size and scaling of the various error terms, including the effect of unequal atomic transition frequencies. Our formalism also allows us to follow the spectral evolution of the field + cavity system in the course of the interaction. [Preview Abstract] |
Friday, June 17, 2011 9:00AM - 9:12AM |
T5.00006: Robust optical delay lines via topological protection Mohammad Hafezi, Eugene Demler, Mikhail Lukin, Jacob Taylor Phenomena associated with topological properties of physical systems are naturally robust against perturbations. This robustness is exemplified by quantized conductance and edge state transport in the quantum Hall and quantum spin Hall effects. Here we show how exploiting topological properties of optical systems can be profitably used in photonic devices. We demonstrate how quantum spin Hall Hamiltonians can be created with linear optical elements using a network of coupled resonator optical waveguides (CROW) in two dimensions. We find that key features of quantum Hall systems, including the characteristic Hofstadter butterfly and robust edge state transport, can be obtained in such systems. As a specific application, we show that the topological protection can be used to dramatically improve the performance of optical delay lines and to overcome limitations related to disorder in photonic technologies. [Preview Abstract] |
Friday, June 17, 2011 9:12AM - 9:24AM |
T5.00007: All-optial quantum ratchet Clinton Thompson, Gautam Vemuri, Girish Agarwal A ratchet is a device in which there is directed motion of a particle in one direction, but in which motion is blocked in the opposite direction. This directed motion is a result of an underlying asymmetry between the potential in which the particle is moving and the quantum mechanical density distribution. Recently, quantum ratchets have been shown in Bose-Einstein condensates where the resultant motion of the particles is due to the asymmetry between the particle's wavefunction and the potential it is moving in. In this paper, we propose a theoretical realization of an all-optical quantum ratchet in a medium composed of an array of coupled waveguides. Such arrays of waveguides have proven to be very useful in studying a number of effects that arise in condensed matter physics and quantum physics. By coupling light into two adjacent waveguides, and calculating the expectation value for the position space operator, we demonstrate the ratchet like behavior of this quantum-mechanical system. [Preview Abstract] |
Friday, June 17, 2011 9:24AM - 9:36AM |
T5.00008: Optically induced parametric magnetic resonances Ricardo Jimenez, Svenja Knappe, John Kitching Optically pumped vector magnetometers based on zero-field resonances have reached very high sensitivities by operating at high atomic densities where dephasing due to spin-exchange collisions can be suppressed [1]. Simplified setups, with just one laser beam have measured magnetic fields from the human brain and heart . A key feature in these magnetometers is the introduction of an rf magnetic field along the measurement axis to generate a parametric resonance. Lock-in detection of the transmitted light, at an odd harmonic of the modulation frequency, allows the reduction of the low frequency noise and generates a resonance with dispersive shape. Here we study a zero-field vector magnetometer where the parametric resonances are induced by the vector AC stark-shift of light. This approach does not produce any external magnetic field that could disturb the reading of other magnetometers in the vicinity and could provide an alternative in applications where an applied AC-field cannot be used. We have characterized the vector AC stark-shift effect of light on Rb atoms contained in a micromachined vapor cell with buffer gas. We have obtained parametric resonances induced by modulation of the light-shift. We also analyze the detunings and intensities of the light-shift beam that maintain the magnetometer within the spin-exchange relaxation-free regime. [1] Allred et al.,Phys.Rev.Lett. 89, 130801 (2002) [Preview Abstract] |
Friday, June 17, 2011 9:36AM - 9:48AM |
T5.00009: Asymptotically optimal lower bounds on confidence for rejecting local realism Yanbao Zhang, Scott Glancy, Emanuel Knill In a test of local realism (LR), the confidence for rejecting LR is usually estimated by comparing Bell-inequality violation to experimental standard deviation (SD). However, it is important to have methods to assign a rigorous confidence to rejecting LR based on experimental data. We propose a method to lower-bound the rejection confidence by a prediction-based ratio test. The test gives a rigorous lower bound even if the prepared quantum state and maximum likelihood LR prediction are allowed to change depending on previous experiments and their outcomes. If the prepared state does not vary in time, the bound is asymptotically optimal. We study violations of LR by unbalanced Bell states $\cos(\theta)|00\rangle+\sin(\theta)|11\rangle$, which are experimentally achievable by a parametric down-conversion photon-pair source within a Sagnac loop. Our results show that the method based on experimental SD gives less confidence than our method when $\theta$ is small, i.e., $\theta<33^{\circ}$, while it gives too much confidence when $\theta$ becomes larger. Given photon-pair production probability, detection efficiency and visibility , numerically we find the optimal states and measurement settings which give the highest confidence gain rate per event. [Preview Abstract] |
Friday, June 17, 2011 9:48AM - 10:00AM |
T5.00010: Entanglement from Longitudinal and Scalar Photons James Franson The covariant quantization of the electromagnetic field in the Lorentz gauge gives rise to longitudinal and scalar photons in addition to the usual transverse photons [1]. This is necessary because the vector and scalar potentials form the components of a four-vector. Quantizing only the transverse components of the field would give different results in different reference frames and is not invariant under Lorentz transformations. Here we calculate the entanglement of two atoms or harmonic oscillators due to the exchange of longitudinal and scalar photons. The form of the entangled state is found to be very different from that obtained using only transverse photons in the Coulomb gauge. Nevertheless, a generalized gauge transformation is used to show that the results are physically equivalent. A covariant treatment of photons is necessary for a fundamental understanding of quantum optics and it may have practical implications for quantum communications between satellites and ground stations, for example. \\[4pt] [1] For example, see C. Cohen-Tannoudji, J. Dupont-Roc, and G. Grynberg, Photons and Atoms (Wiley, New York, 1989.) [Preview Abstract] |
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