Quantum memory for nonstationary light fields based on controlled reversible inhomogeneous broadening (original) (raw)
Physical Review A, 2000
We propose an efficient method for mapping and storage of a quantum state of propagating light in atoms. The quantum state of the light pulse is stored in two sublevels of the ground state of a macroscopic atomic ensemble by activating a synchronized Raman coupling between the light and atoms. We discuss applications of the proposal in quantum information processing and in atomic clocks operating beyond quantum limits of accuracy. The possibility of transferring the atomic state back on light via teleportation is also discussed. 42.50.Lc, 42.50.Dv, 42.50.Ct, 06.30.Ft Light is an ideal carrier of quantum information, but photons are difficult to store for a long time. In order to implement a storage device for quantum information transmitted as a light signal, it is necessary to faithfully map the quantum state of the light pulse onto a medium with low dissipation, allowing for storage of this quantum state. Depending on the particular application of the memory, the next step may be either a (delayed) measurement projecting the state onto a certain basis, or further processing of the stored quantum state, e.g., after a read-out via the teleportation process. The delayed projection measurement is relevant for the security of various quantum cryptography and bit commitment schemes [1]. The teleportation read-out is relevant for full scale quantum computing.
Nature Communications
Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information. A critical figure of merit is the overall storage and retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. Here we report on a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and efficiency around 68%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. Our work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.
Towards high-speed optical quantum memories
2010
Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers [1] and quantum communications . So far, quantum memories have operated with bandwidths that limit data rates to MHz. Here we report the coherent storage and retrieval of sub-nanosecond low intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium vapor. The novel memory interaction takes place via a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field . This allows for an increase in data rates by a factor of almost 1000 compared to existing quantum memories. The memory works with a total efficiency of 15% and its coherence is demonstrated by directly interfering the stored and retrieved pulses. Coherence times in hot atomic vapors are on the order of microseconds [9] -the expected storage time limit for this memory.
Photon echo quantum memory for arbitrary non-stationary light fields
2006
We develop the theory of an optical quantum memory protocol based on the three pulse photon echo (PE) in an optically dense medium with controlled reversible inhomogeneous broadening (CRIB). The wavefunction of the retrieved photon echo field is derived explicitly as a function of an arbitrary input Data light field. The storage and retrieval of time-bin qubit states based on the described quantum memory is discussed, and it is shown that the memory allows to measure the path length difference in an imbalanced interferometer using short light pulses.
Quantum Repeaters with Photon Pair Sources and Multimode Memories
Physical Review Letters, 2007
We propose a quantum repeater protocol which builds on the well-known DLCZ protocol [L.M. Duan, M.D. Lukin, J.I. Cirac, and P. Zoller, Nature 414, 413 (2001)], but which uses photon pair sources in combination with memories that allow to store a large number of temporal modes. We suggest to realize such multi-mode memories based on the principle of photon echo, using solids doped with rare-earth ions. The use of multimode memories promises a speedup in entanglement generation by several orders of magnitude and a significant reduction in stability requirements compared to the DLCZ protocol.
Nonadiabatic approach to quantum optical information storage
Physical Review A, 2001
We show that there is no need for adiabatic passage in the storage and retrieval of information in the optically thick vapor of Lambda-type atoms. This information can be mapped into and retrieved out of long-lived atomic coherence with nearly perfect efficiency by strong writing and reading pulses with steep rising and falling edges. We elucidate similarities and differences between the ''adiabatic'' and ''instant'' light storage techniques, and conclude that for any switching time, an almost perfect information storage is possible if the group velocity of the signal pulse is much less than the speed of light in the vacuum c and the bandwidth of the signal pulse is much less then the width of the two-photon resonance. The maximum loss of the information appears in the case of instantaneous switching of the writing and reading fields compared with adiabatic switching, and is determined by the ratio of the initial group velocity of the signal pulse in the medium and speed of light in the vacuum c, which can be very small. Quantum restrictions to the storage efficiency are also discussed.
Quantum Memory with a Single Photon in a Cavity
Physical Review Letters, 1997
The quantum information carried by a two-level atom was transferred to a high-Q cavity and, after a delay, to another atom. We realized in this way a quantum memory made of a field in a superposition of 0 and 1 photon Fock states. We measured the "holding time" of this memory corresponding to the decay of the field intensity or amplitude at the single photon level. This experiment implements a step essential for quantum information processing operations. [S0031-9007(97)03701-0] PACS numbers: 89.70. + c, 03.65. -w, 32.80. -t, 42.50. -p The manipulation of simple quantum systems interacting in a well-controlled environment is a very active field in quantum optics, with strong connections to the theory of quantum information . Atoms and photons can be viewed as carriers of "quantum bits" (or qubits) storing and processing information in a nonclassical way. The interaction between two qubit carriers can model the operation of a quantum gate in which the evolution of one qubit is conditioned by the state of the other [2,3]. Combining a few qubits and gates could lead to the realization of simple quantum networks in which an "engineered entanglement" between the interacting qubits carriers could be achieved. Even if practical applications to large scale quantum computing are likely to remain inaccessible [4], fundamental tests of quantum theory could be performed, such as demonstrations of new quantum nonlocal effects , decoherence studies, etc.
Quantum memory with optically trapped atoms
Physical review letters, 2008
We report the experimental demonstration of a quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross-correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Non-classical correlations are observed for storage times up to 60 µs.