Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session P9: Quantum Control II |
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Chair: Svetlana Malinovskaya, Stevens Institute of Technology Room: 556AB |
Thursday, May 26, 2016 2:00PM - 2:12PM |
P9.00001: Quantum tomography of near-unitary processes in high-dimensional quantum systems Nathan Lysne, Hector Sosa Martinez, Poul Jessen, Charles Baldwin, Amir Kalev, Ivan Deutsch Quantum Tomography (QT) is often considered the ideal tool for experimental debugging of quantum devices, capable of delivering complete information about quantum states (QST) or processes (QPT). In practice, the protocols used for QT are resource intensive and scale poorly with system size. In this situation, a well behaved model system with access to large state spaces (qudits) can serve as a useful platform for examining the tradeoffs between resource cost and accuracy inherent in QT. In past years we have developed one such experimental testbed, consisting of the electron-nuclear spins in the electronic ground state of individual Cs atoms. Our available toolkit includes high fidelity state preparation, complete unitary control, arbitrary orthogonal measurements, and accurate and efficient QST in Hilbert space dimensions up to $d=$16. Using these tools, we have recently completed a comprehensive study of QPT in 4, 7 and 16 dimensions. Our results show that QPT of near-unitary processes is quite feasible if one chooses optimal input states and efficient QST on the outputs. We further show that for unitary processes in high dimensional spaces, one can use informationally incomplete QPT to achieve high-fidelity process reconstruction (90{\%} in $d=$16) with greatly reduced resource requirements. [Preview Abstract] |
Thursday, May 26, 2016 2:12PM - 2:24PM |
P9.00002: Simulation of an arbitrary quantum channel with minimal ancillary resource Chao Shen, Kyungjoo Noh, Victor V. Albert, Michel H. Devoret, Robert J. Schoelkopf, Steven M. Girvin, Liang Jiang We discuss an explicit and efficient construction of quantum circuits that can simulate an arbitrary given quantum channel acting on a d-level quantum system, with the minimal quantum ancillary resource---a qubit and its QND readout. The elementary operations required are unitary evolutions and single qubit projective measurement. We further show that this technique opens up exciting new possibilities in the field of quantum control, quantum simulation, quantum error correction, and quantum state discrimination. Our proposal can be implemented on platforms such as a superconducting transmon qubit inside a microwave cavity. [Preview Abstract] |
Thursday, May 26, 2016 2:24PM - 2:36PM |
P9.00003: Biphoton Generation Driven by Spatial Light Modulation: Parallel-to-Series Conversion Luwei Zhao, Xianxin Guo, Yuan Sun, Yumian Su, M. M. T. Loy, Shengwang Du We demonstrate the generation of narrowband biphotons with controllable temporal waveform by spontaneous four-wave mixing in cold atoms. In the group-delay regime, we study the dependence of the biphoton temporal waveform on the spatial profile of the pump laser beam. By using a spatial light modulator, we manipulate the spatial profile of the pump laser and map it onto the two-photon entangled temporal wave function. This parallel-to-series conversion (or spatial-to-temporal mapping) enables coding the parallel classical information of the pump spatial profile to the sequential temporal waveform of the biphoton quantum state. The work was supported by the Hong Kong RGC (Project No. 601113). [Preview Abstract] |
Thursday, May 26, 2016 2:36PM - 2:48PM |
P9.00004: Angular resolution of orthogonal polarizations using inhomogeneous control field Shubhrangshu Dasgupta, Pardeep Kumar The control of propagation direction of light by another light through their interaction with the medium has created a new avenue of research, with a special focus on the beam deflection in a homogeneous medium subjected to external fields. The key requirement for such a deflection is the spatial modulation of the refractive index of the medium induced by an inhomogeneous field. Beam deflection has been previously studied inside a medium, where electromagnetically induced transparency (EIT) or active Raman gain (ARG) [C. Zhu {\it et. al.\/}, Phys. Rev. A {\bf 88}, 013841 (2013)] plays the crucial role. Here, we present a theoretical analysis to demonstrate the polarization-dependent light deflection of a weak probe field in a weakly birefringent medium in tripod configuration. We show that by changing the incidence angle of a control field as well as its transverse intensity profile, one can induce quite large ($\sim 100$ mrad) angular divergence to different polarization components of the probe field. We identify that it is the coherent population oscillation (CPO) [S. Kumar {\it et. al.\/}, Phys. Rev. A {\bf 88}, 023852 (2013)] that leads to negligible absorption of the polarization components, contrary to the proposals which rely upon EIT and ARG. [Preview Abstract] |
Thursday, May 26, 2016 2:48PM - 3:00PM |
P9.00005: Controlled Rapid Adiabatic Passage in a V-Type System Yunheung Song, Han-gyeol Lee, Hanlae Jo, Jaewook Ahn In chirped rapid adiabatic passage (RAP), chirp sign determines the final state to which the complete population transfer (CPT) occurs in a three-level V-type system. In this study, we show that laser intensity can be alternatively used as a control means in RAP, when the laser pulse is chirped and of a spectral hole resonant to one of the excited states. We verified such excitation selectivity in the experiment performed as-shaped femtosecond laser pulses interacting with the lowest three levels (5S, 5P$_{1/2}$, and 5P$_{3/2}$) of atomic rubidium. The successful demonstration implies that this intensity-dependent RAP in conjunction with laser beam profile programming may allow excitation selectivity for atoms or ions arranged in space. [Preview Abstract] |
Thursday, May 26, 2016 3:00PM - 3:12PM |
P9.00006: Probing vacuum-induced coherence via magneto-optical rotation in molecular systems Pardeep Kumar, Bimalendu Deb, Shubhrangshu Dasgupta Vacuum-induced coherence (VIC) arises due to the quantum interference between the spontaneous emission pathways from the degenerate excited states to a common ground state. The stringent requirement for the VIC to occur is the nonorthogonality of the transition dipole matrix elements. Unlike atoms, molecules are the promising systems for exploration of VIC, as it is possible to identify the non-orthogonal transitions due to the coupling of the rotation of molecular axis with molecular electronic angular momentum. Usually, the possible signatures of VIC are obtained by manipulating the \textit{absorption} of the probe field. In this paper, we show how the \textit{dispersion} of the probe field can be manipulated to obtain a measurable signature of VIC. Precisely speaking, we explore a way to probe VIC in molecules by observing its influence on magneto-optical rotation (MOR). We show that VIC in the presence of a control laser and a magnetic field can lead to large enhancement in the rotation of the plane of polarization of a linearly polarized weak laser with vanishing circular dichroism. This effect can be realized in cold molecular gases. Such a large MOR angle may be used as a tool for optical magnetometry to detect weak magnetic field with large measurement sensitivity. [Preview Abstract] |
Thursday, May 26, 2016 3:12PM - 3:24PM |
P9.00007: Quantum control in a seven-level system using optical frequency combs modulated from both the temporal and spectral domains Gengyuan Liu, Svetlana Malinovskaya We present a method that makes use of the modulated optical frequency combs to perform two-photon Raman transitions in a stepwise manner in the framework of a semiclassical seven-level system. The phase of optical frequency combs is sinusoidally modulated from both the time domain and the frequency domain. Dressed states analysis is applied to reveal the machanism of adiabatic passage of the population transfer. Odd parity of the spectral and temporal modulation shown to lead to a creation of the dark state, which may have useful applications to mitigate decoherence. A uniformity of quantum control approaches from both the temporal and spectral domains is clarified by using Wigner distribution analysis. [Preview Abstract] |
Thursday, May 26, 2016 3:24PM - 3:36PM |
P9.00008: Trojan Wave Packets in the Quantum Cavity within the Extended Jaynes-Cummings Model Matt Kalinski Some time ago we have developed the theory of the Trojan Wave Packets (TWP) in the classical strong Circularly Polarized electromagnetic field in terms of the Mathieu generating functions. We have discovered that by the proper partitioning of the Coulomb spectrum i.e. by considering the deviation from the circularity and the vertical tilt of the undressed states as the new quantum numbers we can reduce the problem to the problem of several non-interacting quantum pendula for the Stark-Zeeman field dressed states. The TWP in the infinite physical space however turned out to be weakly unstable due to the spontaneous emission. Here we develop the theory in which the TWP is truly eternal when the electromagnetic interactions are considered quantum and the field is confined by the perfect quantum cavity boundary conditions. First we extend the Jaynes-Cummings (JC) model from the two to the infinite number of levels interacting with the one or two perfectly resonant quantum modes of the electromagnetic field. Similarly the model of JC and our previous pendular model the dressed electron-field eigenstates are constructed within the weakly interacting manifolds. Superpositions of those states are possible with the quantum electron density moving on the circular trajectories. [Preview Abstract] |
Thursday, May 26, 2016 3:36PM - 3:48PM |
P9.00009: Observation of the Quantum-Classical Transition via Electron Diffraction Peter Beierle, Herman Batelaan A collimated electron beam with an energy ranging from .5 keV- 5 keV is passed over a 1 cm long conducting surface. The electrons are diffracted from a 100 nm periodic SiN free-standing grating. The surface is place within the electron near-field diffraction distance. The loss of visibility of the far-field diffraction pattern is measured, which indicates the amount of decoherence that the electrons experienced as they passed over the surface. It has been determined through the visibility as a function of the height with respect to the surface that a) one can observe the transition of the electron's behavior between classical and quantum mechanics, b) that our experiment can be used to rule out a classical theoretical model of the surface decohering mechanism (consistent with Hasselbach's work), and c) this experimental setup is simpler than the use of an interferometer. Comparing a silicon to a gold surface, we are in the process of testing a wider array of theoretical models for the mechanism of decoherence. This work is supported by the National Science Foundation under award number 1306565. [Preview Abstract] |
Thursday, May 26, 2016 3:48PM - 4:00PM |
P9.00010: Active Cancellation of Acoustical Resonances with an FPGA FIR Filter Albert Ryou, Jonathan Simon We demonstrate a novel approach to enhancing the closed-loop bandwidth of a feedback-controlled mechanical system by digitally cancelling its acoustical resonances and antiresonances with an FPGA FIR filter. By performing a real-time convolution of the feedback error signal with an arbitrary filter, we can suppress arbitrarily many poles and zeros below 100 kHz, each with a linewidth as small as 10 Hz. We demonstrate the efficacy of this technique by cancelling the six largest resonances and antiresonances of a high-finesse optical resonator piezomechanical transfer function, thereby enhancing the unity gain frequency by more than an order of magnitude. More broadly, this approach is applicable to stabilization of optical resonators, external cavity diode lasers, and scanning tunneling microscopes. [Preview Abstract] |
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