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arXiv:1612.06878 · Physical Review A

Mode invisibility as a nondestructive probe of entangled qubit-cat states

Paulina Corona-Ugalde, Marvellous Onuma-Kalu, Robert B. Mann

Published Sep 27, 2017• 2 citations
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Abstract

We investigate the dynamics for a two-level atomic system entangled with coherent states using the recently developed mode-invisibility technique. Using a quantum two-level probe, we demonstrate a way to nondestructively measure a number of properties between a qubit entangled with a generalized cat state, including the amplitude of the coherent state, the location and relative excitation of the qubit, and the von Neumann entropy. Our results indicate a connection between this last quantity and the interferometric phase shift of the probe, thereby suggesting a possible way to experimentally measure entanglement nondestructively.

DOI
10.1103/physreva.96.033845

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We investigate the dynamics for a two-level atomic system entangled with coherent states using the recently developed mode-invisibility technique. Using a quantum two-level probe, we demonstrate a way to nondestructively measure a number of properties between a qubit entangled with a generalized cat state, including the amplitude of the coherent state, the location and relative excitation of the qubit, and the von Neumann entropy. Our results indicate a connection between this last quantity and the interferometric phase shift of the probe, thereby suggesting a possible way to experimentally measure entanglement nondestructively.
In this communication, two-mode nonlinear coherent states are reviewed and special cases are given. Starting from a three-level atom coupled to two modes of radiation with any form of nonlinearities of the two-mode fields, we derive a Raman-coupled effective Hamiltonian by a unitary transformation, evaluated perturbatively in coupling constants. We use the quantum entropy to measure the degree of entanglement in the time development of an effective two-level atom interacting with two-mode nonlinear-coherent states. The results show that the nonlinearity effect yields the superstructure of atomic Rabi oscillations and the effect of the Stark shift changes the quasiperiod of the field entropy evolution and entanglement between the particle and the field. A possible experimental test of a new effect is proposed.
In this paper, we study the interaction between an effective two-level atom and a three-mode field. The atom and the field are initially in the excited state and finite dimensional trio-coherent state, respectively. For this sytem, we investigate the atomic inversion, the von Neumann entropy, and the atomic Wehrl entropy. We show that there is a connection between all of these quantities. Also, we prove that the atomic Wehrl entropy exhibits a temporal evolution similar to the von Neumann entropy. It is observed that the Stark shift parameter plays an important role on the evolution of these quantities.
Entangled measurement is a crucial tool in quantum technology. We propose a new entanglement measure of multi-mode detection, which estimates the amount of entanglement that can be created in a measurement. To illustrate the proposed measure, we perform quantum tomography of a two-mode detector that is comprised of two superconducting nanowire single photon detectors. Our method utilizes coherent states as probe states, which can be easily prepared with accuracy. Our work shows that a separable state such as a coherent state is enough to characterize a potentially entangled detector. We investigate the entangling capability of the detector in various settings. Our proposed measure verifies that the detector makes an entangled measurement under certain conditions, and reveals the nature of the entangling properties of the detector. Since the precise characterization of a detector is essential for applications in quantum information technology, the experimental reconstruction of detector properties along with the proposed measure will be key features in future quantum information processing.