02138nas a2200181 4500008004100000245011400041210006900155260001500224300001100239490000700250520155000257100002301807700002401830700002301854700002001877700002201897856003701919 2013 eng d00aDynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence
0 aDynamical quantum correlations of Ising models on an arbitrary l c2013/11/07 a1130080 v153 a Ising models, and the physical systems described by them, play a central role
in generating entangled states for use in quantum metrology and quantum
information. In particular, ultracold atomic gases, trapped ion systems, and
Rydberg atoms realize long-ranged Ising models, which even in the absence of a
transverse field can give rise to highly non-classical dynamics and long-range
quantum correlations. In the first part of this paper, we present a detailed
theoretical framework for studying the dynamics of such systems driven (at time
t=0) into arbitrary unentangled non-equilibrium states, thus greatly extending
and unifying the work of Ref. [1]. Specifically, we derive exact expressions
for closed-time-path ordered correlation functions, and use these to study
experimentally relevant observables, e.g. Bloch vector and spin-squeezing
dynamics. In the second part, these correlation functions are then used to
derive closed-form expressions for the dynamics of arbitrary spin-spin
correlation functions in the presence of both T_1 (spontaneous spin
relaxation/excitation) and T_2 (dephasing) type decoherence processes. Even
though the decoherence is local, our solution reveals that the competition
between Ising dynamics and T_1 decoherence gives rise to an emergent non-local
dephasing effect, thereby drastically amplifying the degradation of quantum
correlations. In addition to identifying the mechanism of this deleterious
effect, our solution points toward a scheme to eliminate it via
measurement-based coherent feedback.
1 aFoss-Feig, Michael1 aHazzard, Kaden, R A1 aBollinger, John, J1 aRey, Ana, Maria1 aClark, Charles, W uhttp://arxiv.org/abs/1306.0172v101386nas a2200265 4500008004100000245006600041210006500107260001500172300000900187490000700196520066500203100002100868700001800889700001300907700002100920700001700941700001300958700001100971700001500982700002200997700002301019700001901042700001501061856004401076 2004 eng d00aQuantum key distribution with 1.25 Gbps clock synchronization0 aQuantum key distribution with 125 Gbps clock synchronization c2004/05/17 a20110 v123 a We have demonstrated the exchange of sifted quantum cryptographic key over a
730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude
faster than previously reported results. A classical channel at 1550 nm
operates in parallel with a quantum channel at 845 nm. Clock recovery
techniques on the classical channel at 1.25 Gbps enable quantum transmission at
up to the clock rate. System performance is currently limited by the timing
resolution of our silicon avalanche photodiode detectors. With improved
detector resolution, our technique will yield another order of magnitude
increase in performance, with existing technology.
1 aBienfang, J., C.1 aGross, A., J.1 aMink, A.1 aHershman, B., J.1 aNakassis, A.1 aTang, X.1 aLu, R.1 aSu, D., H.1 aClark, Charles, W1 aWilliams, Carl, J.1 aHagley, E., W.1 aWen, Jesse uhttp://arxiv.org/abs/quant-ph/0405097v1