A high-storage efficiency and long-live quantum memory for photons is an essential component for the information processing in long-distance quantum communication and optical quantum computation. We demonstrated a 78% storage efficiency (SE) of coherent light pulses with a cold atomic medium based on the effect of electromagnetically induced transparency (EIT). We also obtained a large fractional delay of 74 at 50% SE, which is the best record to date. The measured fidelity of the memory is better than 90%. The results suggest the EIT light-matter interface can be readily applied to single-photon quantum states. Our work greatly advances the technology of EIT-based quantum memory for the practical quantum information applications.
A high-storage efficiency and long-live quantum memory for photons is an essential component for the information processing in long-distance quantum communication and optical quantum computation. We demonstrated a 78% storage efficiency (SE) of coherent light pulses with a cold atomic medium based on the effect of electromagnetically induced transparency (EIT). We also obtained a large fractional delay of 74 at 50% SE, which is the best record to date. The measured fidelity of the memory is better than 90%. The results suggest the EIT light-matter interface can be readily applied to single-photon quantum states. Our work greatly advances the technology of EIT-based quantum memory for the practical quantum information applications.
A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation.
Quantum memory is an important component in the long-distance quantum communication system based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 96\% for a photonic memory based on the electromagnetically induced transparency (EIT) scheme in cold atomic media with an optical depth of near 1000. At a storage efficiency of 50\%, we also obtain a fractional delay of 1200. Both are the best record to date in all kinds of the schemes for the realization of quantum memory. Our work significantly advances the pursuit of a high-performance photonic memory and should have important applications in quantum information science.
Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.
Optical quantum memories are important components in the long-distance quantum communication based on quantum repeater protocol. To outperform the direct transmission of light with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and long storage time. Recently, we demonstrate that it is feasible to achieve a high storage efficiency of 92% for electromagnetically-induced-transparency (EIT)-based memory with weak coherent signal pulses in cold atomic ensembles [1]. To realize the highly-efficient memory with quantum light, we have built a bright and narrowband photon-pair source which can be locked to atomic transition based on the cavity-enhanced spontaneous parametric down conversion [2]. Here, we present our results on the storage of single photons generated by such a source in EIT-based memories. A storage efficiency of 36% is obtained in initial runs. Future improvements toward a high efficiency are discussed. Such a development paves the way for the applications of photon-pair-based quantum repeater and multi-photon synchronization.
Quantum storage of flying optical qubits, namely coherently mapping photonic states into and out of an optically controlled memory on demand, constitutes an essential component in the optical quantum information processing science, with applications to long-distance optical communication [1]. In this context, practical protocols require sufficiently large storage efficiency to achieve a performance better than direct transmission. Theoretically, the storage and retrieval efficiency can only be improved with the increase of the optical depth (OD). Recent progresses have shown that high OD media enable to reach high-efficiency electromagnetically induced transparency (EIT)-based optical storage, albeit without the demonstration of qubit storage [2, 3]. Here we experimentally implement an optical quantum memory with single-photon-level probes, showing a EIT-based storage efficiency around 70%. Furthermore, thanks to the spatial multiplexing of the dense atomic ensemble, highly efficient storage of polarization qubit is performed.
Optical quantum memory plays an important role in scaling-up linear optical quantum computations and longdistance quantum communication. For effectively realizing such tasks, a long-lived and highly-efficient quantum memory is needed. The dynamic electromagnetically-induced-transparency (EIT) process can be used for completing an absorptive storage scheme in an atomic ensemble. In such a process, the quantum states of coming single photons can be coherently transformed into spin waves associated with coherences between atomic ground levels via switching off controlling light beam. For storing a single-mode optical signal, a pair of ground levels is involved. While for storing an optical polarization qubit, i.e., two orthogonal polarization modes, the coherence between two pairs of ground levels will be involved. Also, to obtain a high efficiency in the EIT optical storage, the optical-depth of the cold ensemble should be high. For prolonging the coherent time of the spin waves stored in atomic ensemble, decoherence between spin waves due to atomic motion and non-uniform Zeeman shift of ground levels should be effectively suppressed. Recently, a long-lived and highly-efficient optical quantum memory for single-mode storage in a high-optical-depth cold atom ensemble has been experimentally demonstrated via the gradient echo memory scheme (2016 Optical 3 100). While, for the optical polarization qubit storage, a long lifetime (in ms) and high-fidelity EIT storage experiment has been achieved by our group, but the storage efficiency in the experiment is very low (8%) due to lower optical depth of the cold ensemble (2013 Phys. Rev. Lett. 111 240503). The storage efficiency in long-lived storage of two orthogonal polarization modes still needs further improving. Here in this paper we demonstrate an experiment of long-lived and highly-efficient storage of two optical orthogonal polarization modes in a high optical-depth cold atomic ensemble via dynamic EIT process. For achieving a long lifetime in the storage experiment, we follow the two steps, which are used in our previous work (2013 Phys. Rev. Lett. 111 240503). 1) We make the signal and writing-reading light beams collinearly pass through the cold-atom cloud along the z direction to suppress the decoherence between the spin waves due to atomic motion. 2) We apply a moderate magnetic field (13.5 G) to the cold-atom ensemble to lift Zeeman degeneracy. So, the magnetic-field-sensitive transitions are removed from EIT system and the two optical orthogonal polarization modes are stored as two magnetic-field-insensitive spin waves. In contrast to our previous experiment, we finish the storage in the high optical-depth cold atomic ensemble. To obtain such a high optical-depth cold atomic ensemble, we expand the diameters of the trapping laser beams and use a pair of rectangular magnetic coils in a magnetic optical trap (MOT) to prepare a cigar-shaped cold atomic ensemble. The MOT magnetic field is further compressed, and then the optical-depth of the cold atomic ensemble increases up to ~11 in the present experiment, which allows us to achieve a storage efficiency of 30%, which exceeds the previous value (8%). At an MOT repetition rate of 10 Hz, the measured zero-delay storage efficiencies for the two orthogonal polarization modes are symmetric, which go up to ~30%. The 1/e-folding lifetimes of the two orthogonal polarization modes rise up to 3 ms. We also measure the dependence of the zero-delay retrieval efficiency on the MOT repetition rate F and find that the storage efficiency is still more than 20% when the repetition rate F is 50 Hz. The present results will allow one to achieve a long lifetime and highly-efficient quantum memory for photonic polarization qubit and then find applications in scaling-up linear-optical quantum computations and long-distance quantum communication.