Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T27: Open Quantum Systems and Decoherence |
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Sponsoring Units: GQI DAMOP Chair: Michael Zwolak, Los Alamos National Laboratory Room: C155 |
Wednesday, March 23, 2011 2:30PM - 2:42PM |
T27.00001: Landau-Zener-St\"uckelberg interference in the presence of quantum noise Yang Yu, Lingjie Du, Minjie Wang We investigated the Landau-Zener-St\"uckelberg (LZS) interference in strongly driven two-level systems subjected to quantum noise. The transition rate induced by consecutive LZ transitions is obtained, from which LZS interference can be analytically calculated based on rate equation. In the presence of significant frequency dependent noise, the evolving paths of LZS interference is going to be detoured. Therefore, the position of the resonant peaks is shifted and a stationary population inversion in TLS without involving the third qubit state is generated. The LZS interferometry can be used to investigate the noise property hence the decoherence source of the system. In addition, the stationary population inversion may find application in lasing and microwave cooling. [Preview Abstract] |
Wednesday, March 23, 2011 2:42PM - 2:54PM |
T27.00002: Exact master equations for linearly coupled Bosons or Fermions Shao-Wen Chen, Ren-Bao Liu Using the coherent-state representation (P-representation), we derived the exact master equation for a quantum system in an environment, which has linear but otherwise arbitrary couplings. This method works for both Boson and Fermion systems, since the coherent states of Bosons and Fermions have the similar algebra structure. The new derivation reproduces the previous works on photon dynamics in coupled cavities or quantum transport through double quantum dots, but it provides a more general theoretical framework for studying quantum dynamics in photonic, mechanical, and photomechanical systems, and quantum transport in nanostructures. [Preview Abstract] |
Wednesday, March 23, 2011 2:54PM - 3:06PM |
T27.00003: Engineering inverse power law decoherence of a qubit Francesco Petruccione, Filippo Giraldi The exact dynamics of a Jaynes-Cummings model for a qubit interacting with a bath of bosons, characterized by a special form of the spectral density, is evaluated analytically. The special reservoirs are sub-ohmic at low frequencies and inverse power law at high frequencies. The exact dynamics of the qubit is described analytically through Fox H-functions. Over estimated long time scales, decoherence results in inverse power laws with powers decreasing continuously to unity, according to the particular choice of the engineered reservoir. If compared to the exponential-like relaxation obtained from the original Jaynes-Cummings model for Lorentzian-type spectral density functions, decoherence is considerably hindered. [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:18PM |
T27.00004: Decoherence of high-$\ell $ Rydberg wave packets by collisions and electrical noise Brendan Wyker, S. Ye, T. McKinney, F.B. Dunning, S. Yoshida, C.O. Reinhold, J. Burgd{\"o}rfer Quantum revivals in very-high-$n$ ($n\sim $300) high-$\ell $ Rydberg wave packets generated from parent $n$p states are used to examine decoherence induced by collisions and by the application of ``colored'' noise from a random pulse generator. In the absence of external perturbations, the high-$\ell $ wave packets maintain their coherence for periods $\sim $ 1 $\mu $s, i.e., for many hundreds of orbits. However, their coherence can be destroyed on sub-microsecond timescales by the presence of even small amounts of electrical noise at a rate that depends markedly on the spectral characteristics of the noise. In contrast, measurements over similar timescales with CO$_{2}$ target gas at densities of $\sim $ 10$^{11}$ cm$^{-3}$ provide no evidence of collisional dephasing. [Preview Abstract] |
Wednesday, March 23, 2011 3:18PM - 3:30PM |
T27.00005: Non-Markovian trajectory approach of three-level quantum systems Ting Yu, Jun Jing The non-Markovian dynamics of a three-level quantum system coupled to a bosonic environment is a difficult problem due to the lack of an exact dynamic equation such as a master equation. We present for the first time an exact quantum trajectory approach to a dissipative three-level model. We have established a convolutionless stochastic Schr\"{o}dinger equation called time-local quantum state diffusion (QSD) equation without any approximations, in particular, without Markov approximation. Our exact time-local QSD equation opens a new avenue for exploring quantum dynamics for a higher dimensional quantum system coupled to a non-Markovian environment. [Preview Abstract] |
Wednesday, March 23, 2011 3:30PM - 3:42PM |
T27.00006: Manipulating decoherence of a single solid-state spin by quantum control of its spin bath environment Gijs de Lange, Toeno van der Sar, Machiel Blok, Zhihui Wang, Viatcheslav Dobrovitski, Ronald Hanson The coherence of solid-state spins is limited by uncontrolled interactions with their spin environment. High-fidelity single-spin control can be used to prolong the coherence by dynamically decoupling the spin from the environment [see De Lange et al., Science 330, 60 (2010)]. Here, we demonstrate a new approach towards decoherence control based on coherent manipulation of the spin bath environment itself. Our system consists of a single NV center spin in diamond, surrounded by a bath of electronic spins belonging to nitrogen impurities. By driving the bath spins resonantly and using the NV spin as a sensor, we are able to detect all transitions of the bath spins and demonstrate independent quantum control of each of them. This newly gained control opens the door to a number of exciting experiments such as measurement of the spin bath dynamics, manipulation of the spin bath correlation time, decoherence editing, and protection of NV spin coherence by suppressing the dynamics in its spin environment. In this talk we will present our latest results towards these goals. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 3:54PM |
T27.00007: Optical cooling of a 122 kHz mechanical resonator Evan Jeffrey, Petro Sonin, Dustin Kleckner, Brian Pepper, Dirk Bouwmeester We demonstrate radiation pressure cooling of a 122-kHz, 60-ng mechanical resonator in an optical cavity. We use a dilution refrigerator to achieve a low base temperature ($<$ 100 mK). The resonators consist of high reflectivity mirrors suspended on a stressed silicon nitride cross resonator. Due to their low frequency, high Q ($>$40000) and high finesse ($>$ 10000) these devices are excellent candidates for demonstrating quantum behavior of macroscopic systems, with the possibility of achieving quantum superpositions, entanglement with external degrees of freedom, and studying exotic decoherence mechanisms. [Preview Abstract] |
Wednesday, March 23, 2011 3:54PM - 4:06PM |
T27.00008: Long-lived Fermionic Fock-space coherence in quantum dots Eduardo Vaz, Jordan Kyriakidis The Fock-space coherence between quantum states with different particle numbers naturally arising in an open quantum system, qualitatively differs from the more common Hilbert-space coherence between states with the same particle number. For a quantum dot with multiple channels available for transport, we have found specific energy and coupling regimes where a long-lived resonance in the fermionic Fock-space coherence of the system is realized, even where no resonances are found either in the population probabilities or Hilbert-space coherence of the system. We discuss how this resonance in the Fock-space coherence remains robust even in the presence of both boson-mediated relaxation and transport through the quantum dot, as well as its physical origin. [Preview Abstract] |
Wednesday, March 23, 2011 4:06PM - 4:18PM |
T27.00009: Excitation induced dephasing from indistinguishability Peter Bryant In a variety of experiments, Rabi oscillations suffer dephasing that often and perhaps generally depends on the Rabi frequency. This unexpected result has been called excitation induced dephasing. Explanations specific to experiments have been suggested, but here we describe a new approach to the treatment of decoherence and open systems, that allows one to address the indistinguishability of quantum systems. When physical systems are indistinguishable, excitation induced dephasing is a general phenomenon, and a preliminary model shows good agreement with a wide range of experimental results. [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:30PM |
T27.00010: Noise in a Josephson junction qubit due to two-level-systems coupled to a quantum EM field Victor Galitski, So Takei We theoretically study loss of the dielectric film located within an LC resonator circuit due to two-level defects (TLDs). We present a fully quantum mechanical treatment of the full system in which the TLDs couple to a quantized harmonic oscillator, which models the resonator, and to quantized bosonic fields that describe the feedline used to pump and probe the resonator. We focus on the forward transmission as a function of the microwave pump frequency, and investigate how the fluctuating defects affect the noise spectrum of the transmitted voltage signal. Our quantum mechanical treatment makes connections to experiments conducted down to energies where a single photon is stored in the resonator. [Preview Abstract] |
Wednesday, March 23, 2011 4:30PM - 4:42PM |
T27.00011: Suppression of Decoherence and Disentanglement in Qubits via the Exchange Interaction Amrit De, Dong Zhou, Robert Joynt We show that the decoherence and disentanglement for a pair of interacting qubits can be suppressed by the exchange interaction in the presence of one or more uncorrelated random telegraphic noise sources. The suppression of the dissipative dynamics is more apparent for the maximally entangled Bell states, particularly if the noise is non-Markovian. Hence, the entangled singlet-triplet superposition state of two qubits can be protected by the interaction, while for the triplet-triplet state, it is less effective. This makes the former more suitable for encoding quantum information. Our calculations are done using a recently developed quasi Hamiltonian formalism that is suitable for describing non-unitary temporal dynamics in an open quantum system subjected to classical stochastic noise processes. Exact and approximate solutions are obtained for a number of cases. [Preview Abstract] |
Wednesday, March 23, 2011 4:42PM - 4:54PM |
T27.00012: Concatenated Stabilizer Dynamical Decoupling Gerardo Paz Silva, Daniel Lidar We show how to integrate concatenated dynamical decoupling (CDD) techniques with quantum error correction (QEC) codes: the two main strategies to protect quantum information from the decoherence induced by unwanted interaction with the environment. It has been shown that CDD can be used as a lower level protection layer against decoherence and improves the effective error rate of a physical gate, provided one assumes certain locality conditions (local bath assumption) [Ng, Lidar, Preskill, arXiv:0911.3202]. The typical CDD protocol uses pulses from a group of non-commuting operators to decouple to arbitrary order, in the sense of Magnus expansion, the state one wants to protect from the environment. Here, in the same spirit as [Lidar, Phys. Rev. Lett. 100, 160506 (2008)], we show how to decouple a state encoded in some stabilizer QEC code to arbitrary order by applying pulses from the stabilizer group of the QEC code. We demonstrate the technique for concatenated and non-concatenated QEC codes and show that, in contrast to the CDD case, (i) one can omit the local bath assumption, and (ii) has the freedom of simultaneously introducing evolution for the protected state. [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:06PM |
T27.00013: Decoherence and entanglement of a pair of coupled qubits Mohammad Sahrapour, Nancy Makri We analyze the quantum dynamics of a pair of qubits coupled via Ising-type coupling under the influence of a common dissipative bath. We present results of simulations for a range of system biases and spin-spin couplings at two values of bath temperature ($\beta =1,5)$. We also discuss the dynamics of entanglement when starting with fully entangled states and find that for some values of the system parameters, steady-state entanglement is observed. These simulations are carried out via the iterative path integral methodology developed earlier in our group which delivers efficient, numerically exact long time quantum dynamics. [Preview Abstract] |
Wednesday, March 23, 2011 5:06PM - 5:18PM |
T27.00014: Entanglement and Coherence: Differences and Similarities Robert O'Connell Entanglement and coherence both decay due to environmental (heat bath) effects. Apart from the well-known fact that decoherence occurs exponentially and disentanglement occurs with a sudden death, there are many other differences. Here, we concentrate on the effects of temperature T along in the absence of dissipation. Thus, whereas the effect of T on decoherence increases exponentially with time [1], the effect of T on disentanglement is constant for all times [2], reflecting a fundamental difference between the two phenomena. Also, the possibility of disentanglement at a particular T increases with decreasing initial entanglement. Supported in part by NSF under Grant No. ECCS-0757204. \\[4pt] [1] G. W. Ford and R. F. O'Connell, Phys. Lett. A 286, 87 (2001). \\[0pt] [2] G. W. Ford and R. F. O'Connell, Phys. Scr. 82, 038112 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 5:18PM - 5:30PM |
T27.00015: Quantum signatures of chaos in quantum tomography Carlos Riofrio, Vaibhav Madhok, Ivan Deutsch We study the connection between quantum chaos and information gain in the time series of a measurement record used for quantum tomography. The record that is obtained as a sequence of expectation values of a Hermitian operator evolving under repeated application of the Floquet operator of the quantum kicked top on a large ensemble of identical systems. We find that, in the limit of vanishing noise, the fidelities of reconstruction are independent of the underlying chaos of the Floquet map. In the presence of noise, however, the fidelities on an average increase with the chaoticity of the map. Moreover, the number of time steps required to achieve a given fidelity decreases with the increase in the chaoticity, suggesting a connection between the rate of information gain and classical Lyapunov exponents. [Preview Abstract] |
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