Julsgaard Brian, Sherson Jacob, Cirac J Ignacio, Fiurásek Jaromír, Polzik Eugene S
Niels Bohr Institute, Danish Quantum Optics Center-QUANTOP, Copenhagen University, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark.
Nature. 2004 Nov 25;432(7016):482-6. doi: 10.1038/nature03064.
The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot be perfectly recorded in a classical memory, even in principle. In the field of quantum information, this has led to the long-standing challenge of how to achieve a high-fidelity transfer of an independently prepared quantum state of light onto an atomic quantum state. Here we propose and experimentally demonstrate a protocol for such a quantum memory based on atomic ensembles. Recording of an externally provided quantum state of light onto the atomic quantum memory is achieved with 70 per cent fidelity, significantly higher than the limit for classical recording. Quantum storage of light is achieved in three steps: first, interaction of the input pulse and an entangling field with spin-polarized caesium atoms; second, subsequent measurement of the transmitted light; and third, feedback onto the atoms using a radio-frequency magnetic pulse conditioned on the measurement result. The density of recorded states is 33 per cent higher than the best classical recording of light onto atoms, with a quantum memory lifetime of up to 4 milliseconds.
当今通信的信息载体——微弱的光脉冲，本质上是一个量子物体。因此，即使在理论上，关于该脉冲的完整信息也无法完美地记录在经典存储器中。在量子信息领域，这引发了一个长期存在的挑战，即如何将独立制备的光量子态高保真地转移到原子量子态上。在此，我们提出并通过实验演示了一种基于原子系综的量子存储器协议。将外部提供的光量子态记录到原子量子存储器中的保真度达到了70%，显著高于经典记录的极限。光的量子存储通过三个步骤实现：首先，输入脉冲和一个纠缠场与自旋极化的铯原子相互作用；其次，对透射光进行后续测量；第三，根据测量结果使用射频磁脉冲对原子进行反馈。所记录态的密度比将光最佳地记录到原子上的经典记录高出33%，量子存储器寿命长达4毫秒。
