Phase coherence and control of stored photonic information

Abstract

We report the demonstration of phase coherence and control for the recently developed "light storage" technique. Specifically, we use a pulsed magnetic field to vary the phase of atomic spin excitations which result from the deceleration and storing of a light pulse in warm Rb vapor. We then convert the spin excitations back into light and detect the resultant phase shift in an optical interferometric measurement. The coherent storage of photon states in matter is essential for the practical realization of many basic concepts in quantum information processing.The realization of scalable quantum networks for long-distance quantum communication and quantum computation requires the use of photons as quantum information carriers and matter (e.g., spins) as quantum memory elements [1]. For example, intermediate memory nodes will be essential for quantum communication over lossy photonic channels [2,3]. When successfully implemented, such a technique will facilitate secure transmission of secret messages over long distances [4,5]. Likewise, quantum memory elements linked by light are desirable for scalable quantum computation [6].The quantum carrier/memory interface is a key component that should be capable of reversibly transferring quantum states between light pulses and long-lived matter states. In contrast to ordinary "destructive" techniques which convert light into, e.g., electrical signals by photoabsorption, a quantum memory should be free from dissipation and, most importantly, should preserve phase coherence in the process of information transfer to and from the carrier.Recently, proposals have been made to accomplish the quantum transfer of photon states to individual atoms [7] and atomic ensembles [8,9]. Active experimental efforts toward the realization of these ideas are currently under way [10,11]. In particular, recent experiments employing cold Na atoms [12] and warm Rb vapor [13] demonstrated the basic principle of the "storage of light" in atomic ensembles by the dynamic and reversible reduction of the light pulse group velocity to zero.In this Letter we present the first experimental evidence that this light storage technique is phase coherent. Although anticipated from theoretical predictions [8,9], this essential feature of a quantum memory for light has not been verified experimentally up to now. In addition, we demonstrate that the phase of the stored coherence can be accurately manipulated during the storage interval and then mapped coherently onto the released light pulse. These results show that the present technique should be suitable for applications in quantum information processing. For example, a specific "quantum repeater" protocol, which allows for scalable quantum communication over very long distances using this technique, has already been proposed [14]. Scalable quantum computation using atomic ensembles coupled by light has also been suggested [15].The light storage technique is based on the phenomenon of Electromagnetically Induced Transparency (EIT) [16], in which an external o...

Electromagnetically induced left-handedness in a dense gas of three-level atoms

“…Recent advances such as slowing down [1] or stopping light [2], or left handed metamaterials [3] promise advances in fields ranging from optics [4] to quantum computation [5]. It is desirable to find new materials in which electromagnetic waves exhibit novel behavior, and there is a flurry of activity both theoretically and experimentally in this direction.…”

Untitled

“…The dependence of the relaxation rate on the light intensity will be evidently revealed in the fact that the length of this 'tail' will vary with the pump beam intensity (see, e.g., [34]). In our opinion, this natural manifestation of the relaxation properties of a polarization nonlinear absorber may be considered as the effect of polarization memory, but there are no grounds to consider it as 'stopped light' as it is done in many papers on 'slow light' where a degenerate Λ-scheme is used (see., e.g., [30,31,[35][36][37]; for more detail see [13,14]). …”

Complete population transfer in a degenerate three-state atom

“…An extension of this method might also used for control transitions in high Rydberg states [33], including adiabatic rapid passage [34,35]. RWA is used to describe coherent storage of information in photonic states [13]. The approach developed here may be useful for modeling information transmission and storage in atomic states [10] in a new way.…”

“…Population control in quantum systems, namely transfer of electrons from an ensemble of atoms all in the same initial state to specified final states, is used in problems ranging from coherent population trapping [1, 2,3,4,5], including electromagnetically induced transparency [6,7,8,9], and quantum computing [10,11,12,13,14,15,16], to chemical dynamics [17,18]. These problems are modeled in terms of an n-level (often 3-level) atom interacting with a strong external field [19,20,21,22,23,24].…”