Nonexistence of entanglement sudden death in dephasing of high NOON states

Abstract

We study the dynamics of entanglement in continuous variable quantum systems. Specifically, we study the phenomena of entanglement sudden death (ESD) in general two-mode-N-photon states undergoing pure dephasing. We show that for these circumstances, ESD never occurs. These states are generalizations of the so-called high NOON states (i.e., a superposition of N photons in the first mode, O in the second, with O photons in the first, N in the second), shown to decrease the Rayleigh limit of lambda to lambda/N, which promises great improvement in resolution of interference patterns if states with large N are physically realized [Phys. Rev. Lett.85, 2733 (2000)]. However, we show that in dephasing NOON states, the time to reach some critical visibility Vcrit, scales inversely with N2. On the practical level, this shows that as N increases, the visibility degrades much faster, which is likely to be a considerable drawback for any practical application of these states.

Fisher information of a squeezed-state interferometer with a finite photon-number resolution

“…This number resolution is large enough to realize the global phase estimation for the coherentstate input n ≃ 1. Based upon a Bayesian protocol [19], the achievable phase sensitivity was found almost saturating quantum Cramér-Rao bound over a wide phase interval, in agreement with the theoretical prediction F(ϕ) = F Q = n. To realize higher-precision optical metrology, it requires a bright nonclassical light source with larger mean photon number [15], low photon loss [14,[36][37][38] and low noise [39][40][41][42][43][44][45][46][47][48][49][50], as well as the photon counters with high detection efficiency [51] and large enough number resolution. Q,opt as a function of N res /n for given values of n, using the optimal condition that maximizes Eq.…”

Decoherence effects in interacting qubits under the influence of various environments

“…Moreover sudden birth of entanglement has also been predicted for structured heat baths [55,56] and certain choice of initial conditions of the entangled qubits [57]. In another recent work it has been shown that under a pure dephasing environment for a general two mode N-photon state ESD does not occur [58]. This result was explicitly proven for a general 3-photon state of the form |Ψ = a|30 + b|21 + c|12 + d|03 .…”

Quantum interferometry with binary-outcome measurements in the presence of phase diffusion

“…1). Formally, the presence of phase noise can be modeled by the following master equation [17][18][19][20][21][22][23][24][25]:…”

“…This conclusion is independent of the input states and the presence of noises. Next, we investigate the role of phase diffusion [17][18][19][20][21][22][23][24][25] on the binary-outcome homodyne detection, the parity measurement, and the Z measurement. Our analytical results show that the diffusion plays a role in a form of Nγ, rather than the phase-diffusion rate γ and the mean photon number N alone.…”