Fidelity of electromagnetically-induced-transparency-based optical memory

Yi-Hsin Chen, Meng-Jung Lee, I-Chung Wang, and Ite A. Yu

Phys. Rev. A 88, 023805 – Published 5 August 2013

Abstract

Storing light based on the effect of electromagnetically induced transparency (EIT) provides a coherent way to transfer wave functions between photons and matters. The storage device is promising for the application of quantum memory. An important figure of merit for optical memory is fidelity, which can be degraded by either a two-photon detuning or an axial magnetic field gradient in the EIT scheme. We systematically studied the phase of readout light pulses with the beat-note interferometer. The detuning induces a nonuniform phase variation during the pulse propagation and a uniform phase shift during the light storage; in addition, the field gradient induces a nonuniform phase variation during the storage. We further demonstrated that the phase measurement can be used to diagnose a two-photon detuning below 10 kHz (or 1/600 of the excited-state natural linewidth) and a magnetic field gradient as low as 2 mG/cm. The fidelity of the readout pulse from the EIT memory can be achieved to 0.94. Our work provides useful information for practical applications of EIT-based quantum memory and advances the knowledge of EIT-related research fields.

Received 14 April 2013

DOI:https://doi.org/10.1103/PhysRevA.88.023805

Authors & Affiliations

Yi-Hsin Chen^*, Meng-Jung Lee, I-Chung Wang, and Ite A. Yu^†

Department of Physics and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan

^*Corresponding author: yhchen920@gmail.com
^†Corresponding author: yu@phys.nthu.edu.tw

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Vol. 88, Iss. 2 — August 2013

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Images

Figure 1
(a) Relevant energy levels and laser excitations in the experiment. (b) Schematic experimental setup. PD1 and PD2: photodetectors; BS: cubed beam splitter; Coils: magnetic coils. (c) Diagrammatically represents the energy splitting of two ground states $| 1 〉$ and $| 2 〉$ under positive magnetic field gradient (solid lines) and static dc field (dashed lines). $g_{1}$ and $g_{2}$ denote the Landé $g$ -factors.Reuse & Permissions
Figure 2
(a) Phase variation within $e^{- 2}$ full width ( $\pm$ 2.2 $μ s$ ) of the output pulse. $δ$ are $- 83$ , $- 13$ , and 47 kHz shown in black circles, red squares, and blue triangles, respectively. The solid lines are the relative linear fits. (b) Slope of phase variation $η$ as a function of two-photon detuning. The red solid line is the theoretical simulation under the sets of $α = 85$ and $Ω_{c} = 0.58 Γ$ .Reuse & Permissions
Figure 3
$δ / η$ versus ${(Δ ω_{EIT} / Δ ω_{pulse})}^{2}$ . We fix $Ω_{c}$ $=$ 1 $Γ$ and $τ$ $=$ $48 (1 / Γ)$ , and vary $α$ from 15 to 290 shown in red diamonds; fix $α$ $=$ 100 and $τ$ $=$ $48 (1 / Γ)$ , and vary $Ω_{c}$ from 0.74 to 1.60 $Γ$ shown in black circles; and fix $Ω_{c}$ $=$ 1 $Γ$ and $α$ $=$ 100, and vary $τ$ from 26 to 122 $Γ$ shown in blue squares. The dashed line is a linear function of $y = 1 + x$ .Reuse & Permissions
Figure 4
Phase around the peak of the output pulse versus storage time. The solid line is the best linear fit with the slope of 126 kHz, i.e., two-photon detuning.Reuse & Permissions
Figure 5
The red circles and black squares are the experimental data of $η$ versus storage time when the magnetic field gradient existed and was closed to zero, respectively. The black solid line is denoted as no additional phase variation produced in the storage duration. The red solid line is the numerical best fit with $α = 93$ , $Ω_{c} = 0.62 Γ$ , and $β$ $=$ 23 mG/cm. The blue, orange, and green dashed lines are other simulation lines under the same conditions except for $β$ $=$ 10, 20, and 30 mG/cm, respectively. Inset: Fix 10 $μ$ s storage time, SPV is linearly dependent on $β$ .Reuse & Permissions
Figure 6
(a) Beat notes of the input (black) and the retrieved pulses after 7 $μ$ s (red) storage time. The yellow dashed lines are the Gaussian fits of the input and readout pulses, and the green dashed line denotes as the timing of the coupling field. (b) The components of $E_{in} (t - t_{d})$ and $E_{out} (t)$ in the beat-note signals. The dashed lines show the integrating range within the $e^{- 2}$ input pulse width. The obtained fidelity was 0.94. (c) Zooming in on the 200-ns time interval around the pulse peaks.Reuse & Permissions

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