Experimental study of decoherence of the two-mode squeezed vacuum state via second harmonic generation

Open Access

Experimental study of decoherence of the two-mode squeezed vacuum state via second harmonic generation

Fu Li, Tian Li, and Girish S. Agarwal

Phys. Rev. Research 3, 033095 – Published 27 July 2021

Abstract

Decoherence remains one of the most serious challenges to the implementation of quantum technology. It appears as a result of the transformation over time of a quantum superposition state into a classical mixture due to the quantum system interacting with the environment. Since quantum systems are never completely isolated from their environment, decoherence therefore cannot be avoided in realistic situations. Decoherence has been extensively studied, mostly theoretically, because it has many important implications in quantum technology, such as in the fields of quantum information processing, quantum communication, and quantum computation. Here we report a novel experimental scheme on the study of decoherence of a two-mode squeezed vacuum state via its second harmonic generation signal. Our scheme can directly extract the decoherence of the phase-sensitive quantum correlation $〈 \hat{a} \hat{b} 〉$ between two entangled modes $a$ and $b$ . Such a correlation is the most important characteristic of a two-mode squeezed state. More importantly, this is an experimental study on the decoherence effect of a squeezed vacuum state, which has been rarely investigated.

Received 11 December 2020
Accepted 15 July 2021

DOI:https://doi.org/10.1103/PhysRevResearch.3.033095

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Quantum optics

Atomic, Molecular & Optical

Authors & Affiliations

Fu Li^1,2,*,†, Tian Li ^1,3,*,‡, and Girish S. Agarwal^1,2,3

¹Institute for Quantum Science and Engineering, Texas A&M University, College Station, Texas 77843, USA
²Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
³Department of Biological and Agricultural Engineering, Texas A&M University, College Station, Texas 77843, USA

^*These authors contributed equally to this work.
^†fuli@physics.tamu.edu
^‡tian.li@tamu.edu

Article Text

Click to Expand

References

Click to Expand

Issue

Vol. 3, Iss. 3 — July - September 2021

Subject Areas

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Theoretical decoherence characterization of the TMSV state via its SHG signal. To isolate the effect of decoherence on the quantum correlation $〈 \hat{a} \hat{b} 〉$ , the experiment is performed by holding power $p$ constant, i.e., $p \equiv p_{0}$ .
Reuse & Permissions
Figure 2
(a) Experimental setup in which a CW laser-pumped ${}^{85}{Rb}$ vapor cell produces a TMSV state via the FWM process. The TMSV beam (i.e., the “light cone”) is separated from the pump beam by a $\sim 2 \times 10^{5} : 1$ polarizing beam splitter after the cell. The SHG signal from the BBO crystal is collected by an EMCCD camera. Two low-pass filters are mounted in front of the camera to eliminate undesired excitation photons. The BBO crystal and the EMCCD camera are enclosed in a light-proofing box to block ambient light. PBS, polarizing beam splitter; ND, neutral density filter; LP, low-pass filter. (b) Level structure of the D1 transition of ${}^{85}{Rb}$ atom. The optical transitions are arranged in a double- $Λ$ configuration, where $ν_{p}, ν_{c}$ , and $ν_{1}$ stand for probe, conjugate, and pump frequencies, respectively, fulfilling $ν_{p} + ν_{c}$ = $2 ν_{1}$ and $ν_{c} - ν_{p} = 2 ν_{H F}$ . The width of the excited state in the level diagram represents the Doppler-broadened line. $Δ$ is the one-photon detuning; $ν_{HF}$ is the hyperfine splitting in the electronic ground state of ${}^{85}{Rb}$ . (c) An image of the cross-section of the TMSV state, i.e., the light cone, where the bright central spot is the residual pump beam. The angular separation between the center of the ring and the center of the residual pump beam is $\sim 0 . 3^{\circ}$ , and the width of the ring is measured to be $\sim 0 . 05^{\circ}$ .
Reuse & Permissions
Figure 3
TMSV beam (light cone) power as a function of pump power. The dashed line is the theoretical fit according to Eq. (8) with $r \equiv α P$ , where $P$ is the pump power.
Reuse & Permissions
Figure 4
SHG signal as a function of the power of the light cone [shown in Fig. 2 as the “ring”). The dashed line is a polynomial fit according to Eq. (17) with $ND = 0$ .
Reuse & Permissions
Figure 5
SHG signals induced by 80 $μ W$ partially decoherent TMSV beams of light (blue dots, left-hand side of the $y$ axis) and $80 μ W$ coherent beams of light (red dots, right-hand side of the $y$ axis) as a function of transmission of ND filters. The dashed blue line is the theoretical fit according to Eq. (17).
Reuse & Permissions
Figure 6
The mean number of photon difference in percentile at the exit of the cell between $α_{a} = 0.1$ and $α_{a} = 0$ versus the FWM gain G(t=1) for (a) probe mode, $({〈 {\hat{a}}^{†} \hat{a} 〉}_{t = 1, α = 0} - {〈 {\hat{a}}^{†} \hat{a} 〉}_{t = 1, α = 0.1}) / {〈 {\hat{a}}^{†} \hat{a} 〉}_{t = 1, α = 0}$ , and (b) conjugate mode, $({〈 {\hat{b}}^{†} \hat{b} 〉}_{t = 1, α = 0} - {〈 {\hat{b}}^{†} \hat{b} 〉}_{t = 1, α = 0.1}) / {〈 {\hat{b}}^{†} \hat{b} 〉}_{t = 1, α = 0}$ . (c) The expectation value difference in percentile for the quantum correlation $| 〈 \hat{a} \hat{b} 〉 |$ between $α_{a} = 0.1$ and $α_{a} = 0$ , i.e., $(| 〈 \hat{a} \hat{b} 〉 |_{t = 1, α = 0} - | 〈 \hat{a} \hat{b} 〉 |_{t = 1, α = 0.1}) / | 〈 \hat{a} \hat{b} 〉 |_{t = 1, α = 0}$ , versus the FWM gain.
Reuse & Permissions

Physical Review Research