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The European Physical Journal Plus

Quantum state storage in a travelling dark-state polariton under a standing wave control laser field in a solid-state medium

Avirup Chakraborty, Shrabana Chakrabarti

Published Aug 13, 2024• 1 citation
Publisher

Abstract

In this paper, we derive an expression for the dark-state polariton field, formed by the superposition of atomic and photonic states, for the case of a travelling probe laser pulse under the application of a standing wave control laser pulse for a lambda-level scheme EIT System in a solid crystal. We show how an enhancement in the nonlinearity of the EIT process by eliminating pulse broadening due to diffusion can be achieved in the case of a travelling probe pulse under the effect of standing wave control laser pulses. At last, we propose an experiment that can help realise the storage of a probe pulse in the hyperfine levels 3 H 4 ↔ 1 D 2 of Pr 3+ : Y 2 SiO 5, cryogenically cooled at 4.5 K. We, at last, predict from the temporal variation of the energy density of the stored probe pulse that a longer storage time of the travelling probe pulse is possible for a perfect standing wave control laser field than a non-standing control wave, due to its more prominent nonlinear effect.

DOI
10.1140/epjp/s13360-024-05521-4

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Storing quantum information in a solid using dark-state polaritons

Mattias Johnsson, Klaus Mølmer

The possibility of using a solid medium to store few-photon laser pulses as coupled excitations between light and matter is investigated. The role of inhomogeneous broadening and nonadiabaticity are considered, and conditions governing the feasibility of the scheme are derived. The merits of a number of classes of solid are examined.

arXiv:quant-ph/0312130•Physical Review A•Sep 22, 2004•36 citations
In this paper, we derive an expression for the dark-state polariton field, formed by the superposition of atomic and photonic states, for the case of a travelling probe laser pulse under the application of a standing wave control laser pulse for a lambda-level scheme EIT System in a solid crystal. We show how an enhancement in the nonlinearity of the EIT process by eliminating pulse broadening due to diffusion can be achieved in the case of a travelling probe pulse under the effect of standing wave control laser pulses. At last, we propose an experiment that can help realise the storage of a probe pulse in the hyperfine levels 3 H 4 ↔ 1 D 2 of Pr 3+ : Y 2 SiO 5, cryogenically cooled at 4.5 K. We, at last, predict from the temporal variation of the energy density of the stored probe pulse that a longer storage time of the travelling probe pulse is possible for a perfect standing wave control laser field than a non-standing control wave, due to its more prominent nonlinear effect.
We theorize a quantum memory based on the dark-state polariton field, formed by the superposition of atomic and photonic states of a travelling probe laser pulse under the application of standing wave modes of a dominant control laser pulse using a lambda-level scheme Electromagnetically Induced Transparency in a solid medium. We show how an enhancement in the storage time for the pulse is achieved by eliminating pulse broadening due to diffusion. At last, we propose an experiment that can help realize the storage of a probe pulse in the hyperfine levels 3H4↔1D2^3\text{H}_4 \leftrightarrow ^1\text{D}_23H4​↔1D2​ of Pr3+:Y2SiO5\text{Pr}^{3+}:\text{Y}_2\text{SiO}_5Pr3+:Y2​SiO5​, cryogenically cooled at 4.5 K4.5\text{ K}4.5 K. We also discuss multiple applications the storage of the quantum states the probe pulse with a prolonged time interval must have.
This thesis presents theoretical models and results of numerical simulations describing the propagation of optical pulses through dense, thermal atomic vapours. In particular we investigate the nonlinear effects of optical solitons due to self-induced transparency (SIT) in two-level systems, optical simultons in V-type three-level systems and electromagnetically induced transparency (EIT) in Λ-type systems, including the storage and retrieval of dark-state polaritons. An investigation is made into two-photon excitation of the 5D states of rubidium in a high-intensity beam including the hyperfine structure of the relevant atomic levels. Decay from these states to the 6P manifolds is ruled out as a cause of experimentally observed fluorescence due to the amount of power broadening associated with intensities necessary to provide any significant level of population in these highly excited states. We combine the nonlinear effects of optical solitons and EIT to explain experimentally observed steepened pulses in a V-type system in a micron-length cell. We explain the behaviour as the early formation of a simulton pulse drawn from a CW probe field by a strong coupling pulse, due to coherent population trapping. We predict that in a longer cell it may be possible to facilitate propagation of matched pulses, even when the transitions in the system have different propagation coefficients, as long as decoherence from collision broadening can be controlled. The fact that weak pulses can propagate with this scheme suggests an approach to achieving transparent propagation of single or few photon pulses distinct from, but related to, both SIT and EIT.
We investigate light storage by electromagnetically induced transparency in a Pr3+{}^{3+}3+:Y2{}_{2}2​SiO5{}_{5}5​ crystal. The retrieval efficiency versus storage time shows pronounced oscillations, which are due to beating of dark-state polaritons in multiple Zeeman-shifted $\ensuremath{\Lambda}$ systems. As a significant obstacle for applications, the beating leads to periodic collapses of the retrieved signal. We demonstrate how to systematically control the perturbing oscillations in the retrieval efficiency by external magnetic fields. This enables suppression of collapses and retrieval of stored data at any storage time, approaching the limit set by the coherence time in the medium.
We experimentally demonstrate the slowing and storage of double light pulses in a Pr(3+):Y(2)SiO(5) crystal using a multilevel-tripod scheme. Owing to double dark-state polaritons of the tripod-type system, two signal pulses can be simultaneously slowed. Also, we realize the simultaneous storage (and retrieval) of double light pulses by switching off (and back on) the control field. Slowing and storage of double light pulses in solids may have practical applications in quantum information and quantum networks.
The research project dealt with the implementation of EIT light storage in the solid state medium Pr:YSO for storage of single photons on a microsecond timescale and weak coherent pulses on a timescale of seconds. The main challenge was to maintain a large efficiency at long storage times and suppress control pulse background by about 120 dB to enable detection of signals on the single photon level. We used a configuration with counterpropagating probe and control beams which enabled a control pulse suppression of about 80 dB and achieved the remaining suppression by spectral filtering. Since the signal and control read pulse frequencies differ only by ∼10 MHz, we built a filter based on a second Pr:YSO crystal in which we tailored the absorption spectrum to the experimental requirements by optical pumping. For short storage times of 2 μs, the filter enhanced the separation between the signal and control read pulses by 42 dB. This enabled the storage of a weak coherent pulse with an average photon number of 1.1 with an efficiency of 42% and a SNR of 3.2. The efficiency was limited by the OD of the storage medium and could be increased by a multipass setup. Residual leakage of the control pulse through the filter limited the SNR. Still, to the best of our knowledge, our result represents the first implementation of single photon storage based on EIT in a solid state medium. To prolong the coherence lifetime, we implemented ZEFOZ. The influence of the magnetic field reduced the OD of the Pr:YSO crystal which led to a lower storage efficiency. We characterized light storage under ZEFOZ conditions at a short storage time of 2 μs. By application of a multipass setup with three passes and temporal shaping of the probe pulse, we partially compensated the reduced OD and achieved efficiencies of up to 23% for storage of classical light pulses. In order to maintain a high setup transmission, we used only two passes for storage of weak coherent pulses. We demonstrated storage of a weak coherent pulse with an average of 10.2 photons for 2 μs with 16% efficiency and a SNR of 1.3. Again, leakage of the control read pulse through the spectral filter limited the SNR. We found this leakage to be due to a weak but spectrally broad pedestal in the spectrum of our OPO-SFG laser system. In order to prolong the light storage time and exploit the long coherence lifetime under ZEFOZ conditions, we applied different sequences for rephasing with RF pulses. In the design of our RF coils for rephasing, we had to consider restrictions given by the static magnetic field setup. Therefore, the rephasing π pulses had a significant inhomogeneity which led to a low rephasing efficiency of 15% when we applied two π pulses. To compensate these errors, we applied UR DD which increased the rephasing efficiency to 40%. Due to an experimental limitation, we could not reduce the separation of the rephasing π pulses below 10 ms without reducing the storage efficiency. This limited the effectiveness of DD. Nevertheless, we achieved a storage time of 7.5 s for classical light pulses and confirmed this timescale for storage of weak coherent pulses with an average of 52 photons. We stored weak coherent pulses with different photon number for 1.28 s and extrapolated a SNR of 0.09 for storage of a single photon. For storage of a weak coherent pulse with an average of 7 photons, we determined an efficiency of 6% and a SNR of 0.6. This represents the first implementation of a memory for weak coherent pulses close to the single photon level with a storage time in the regime of seconds. Compared to the current state-of-the-art single photon storage time of 100 ms, we achieve a more than one order of magnitude longer storage time. As an extension of our investigations, we developed, implemented and studied novel universal composite pulse sequences to invert superposition states or efficiently transfer population between two states. In particular, we experimentally demonstrated UCPs for population inversion which are especially suited for situations in which pulse area and detuning errors are correlated. We showed that we can rotate the excitation profile of the sequence by changing the phases of the excitation pulses. This enables adaption to the specific correlation of errors present in an experiment. Moreover, we demonstrated a composite version of STIRAP. We showed that for detuned pulses, the phases of UCPs enhance the robustness to variations in any experimental parameter. We achieved an increase in population transfer efficiency from 50% for five times repeated detuned STIRAP to 85% for UR CSTIRAP.