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arXiv:quant-ph/0403102 · Journal of Optics B Quantum and Semiclassical Optics

Analysis of quantum light memory in atomic systems

Hassan Kaatuzian, Ali Rostami, Ahmad Ajdarzadeh Oskouei

Published May 16, 2005• 9 citations
arXivHTMLPDF

Abstract

We extend the theory to describe the quantum light memory in type atoms with considering (lower levels coherency decay rate) and detuning for the probe and the control fields. We obtain that with considering these parameters, group velocity of the probe pulse does not tend to zero by turning off the control field. We show that there are considerable decay for the probe pulse and the stored information. Also, it is inferred that the light field does not tend to zero when the control field is turned off. In addition, we obtain that in the off-resonance case there is considerable distortion of the output light pulse (with fast oscillations) that destroys the stored information. Then we present the limitations on detuning (bandwidths) of the probe and the control fields to achieve negligible distortion. We finally present the numerical calculations and compare them with obtained analytical results.

DOI
10.1088/1464-4266/7/6/001

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We extend the theory to describe the quantum light memory in type atoms with considering (lower levels coherency decay rate) and detuning for the probe and the control fields. We obtain that with considering these parameters, group velocity of the probe pulse does not tend to zero by turning off the control field. We show that there are considerable decay for the probe pulse and the stored information. Also, it is inferred that the light field does not tend to zero when the control field is turned off. In addition, we obtain that in the off-resonance case there is considerable distortion of the output light pulse (with fast oscillations) that destroys the stored information. Then we present the limitations on detuning (bandwidths) of the probe and the control fields to achieve negligible distortion. We finally present the numerical calculations and compare them with obtained analytical results.
We extend the theory of quantum light memory in atomic ensemble of Lambda type atoms with considering lower levels coherence decay rate and one and two-photon detunings from resonances in low intensity and adiabatic passage limit. We obtain that with considering these parameters, that there will be a considerable decay of probe pulse and stored information; also, we obtain that the group velocity of probe (light) pulse and its amplitude does not tend to zero by turning off the control field. We propose a method to keep the probe pulse in small values in turn off time of control field and to reduce the loss of the stored probe pulse. In addition, we obtain that in the Off-resonance case there will be a considerable distortion of the output light pulse that causes in loss of the stored information, then we present limitations for detunings and therefore for bandwidths of practical lasers also limitations for maximum storage time to have negligible distortion of stored information. We finally present the numerical calculations and compare them with analytical results.
We extend the theory of quantum light memory in atomic ensemble of Lambda type atoms with considering lower levels coherency decay rate and one and two-photon detunings from resonances in low intensity and adiabatic passage limit. We obtain that with considering these parameters, group velocity of probe (information) pulse and its amplitude does not tend to zero by turning off the control field, therefore there is no complete storage of light. Also, we obtain that there will be a considerable decay of probe pulse and stored information. We calculate the minimum velocity and decay rate for probe (information) pulse. In addition, we obtain that in the Off-resonance case there will be a considerable distortion of the output light pulse that causes in loss of the stored information, then we present limitations for detunings and therefore for bandwidths of practical lasers also limitations for maximum storage time to have negligible distortion of stored information. We finally present the numerical calculations and compare them with analytical results.
We consider storage and retrieval of light based on electromagnetically induced transparency in an atomic medium using nonadiabatic switching of a control field. We derive various conditions for writing (and reading) the light information to (and from) the atomic coherence. We obtain an analytical solution for the retrieval of the stored pulse that is in excellent agreement with the full numerical results. We identify the origin of distortion at the output and derive a condition to correct the distortions by manipulating the retrieval process.
The emergence of quantum physics from the page to the lab and the world at large is an exciting development of recent years. The prospects of absolutely secure communication and efficient simulation of physical systems have spurred great human effort into understanding these possibilities and turning them into realities. Photons are the most easily manipulated quantum particles and are a promising candidate for implementing these technologies. Limitations of photons include the difficulty of keeping objects that move at the speed of light, and producing strong interactions between particles that do not normally interact. The work presented in this thesis is motivated by the possibility of overcoming these limitations. The ability to faithfully store and reproduce a quantum state is essential for many quantum information technologies. Quantum memories for light have been developed over the last two decades to provide this ability. The group at the Australian National University developed the gradient echo memory (GEM): A quantum state of light can be controllably stored and released from an atomic ensemble by the use of additional optical fields and magnetic field gradients. This scheme was previously shown to preserve the quantum characteristics of the light. We used the GEM scheme with a cold rubidium ensemble to create the first optical memory that simultaneously beat the no-cloning limit, a benchmark for many of the technologies relying on quantum memories, and the loss rate for a delay line composed of optical fibre. We also created an analogue to a pulsed optical resonator using GEM with a warm rubidium vapour. This was done by replacing the circulating optical field of a resonator with light stored in the memory, and replacing the coupling of light into and out of that circulating mode with storage and recall from the memory. The bandwidth and repetition rate of this resonator were rapidly tunable as they were controlled by external optical and magnetic fields. We worked on implementing GEM with strings of thousands of atoms strongly coupled to the evanescent field of an optical nanofibre. This raised new possibilities for creating a true random access memory that would allow a more flexible use of the multi-mode capacity of GEM. We developed the theory for a novel type of stationary light in the gradient echo memory. Our stationary light scheme relies on the destructive interference of counter-propagating optical fields throughout the memory. The optical intensity scales with optical depth, as with other forms of stationary light. However, as the destructive interference could be set up over a much greater distance, more of the optical depth is available for generating stationary light. Finally, we studied how a control-phase gate for single-photon optical states could be implemented using a nonlinear interaction with stationary light. The stationary light generated by one state modulates the phase of another state stored in the memory. The second state modifies the stationary light, also producing a back-action on the first state and generating the required cross-phase shift.
We consider a quantum memory scheme based on the conversion of a signal pulse into a long-lived spin coherence via stimulated off-resonant Raman process. For a storing medium consisting of alkali-metal atoms, we have calculated the Autler-Townes resonance structure created by a strong control field. By taking into account the upper hyperfine states of the D1{D}_{1}D1​ optical transition, we show important deviations from the predictions of the usual three-level $\ensuremath{\Lambda}$-scheme approximation and we demonstrate an enhancement of the process for particular detunings of the control. We estimate the memory efficiency one can obtain using this configuration.
We study the coherent storage and retrieval of a very short multimode light pulse in an atomic ensemble. We consider a quantum memory process based on the conversion of a signal pulse into a long-lived spin coherence via light matter interaction in an on-resonant $\ensuremath{\Lambda}$ -type system. In order to study the writing and reading processes we analytically solve the partial differential equations describing the evolution of the field and of the atomic coherence in time as well as in space. We show how to optimize the process for writing as well as for reading. If the medium length is fixed, for each length, there is an optimal value of the pulse duration. We discuss the information capacity of this memory scheme and we estimate the number of transverse modes that can be stored as a quantum hologram.