Heralded Single-Magnon Quantum Memory for Photon Polarization States

Abstract

We demonstrate a heralded quantum memory based on mapping of a photon polarization state onto a single collective-spin excitation (magnon) shared between two spatially overlapped atomic ensembles. The polarization fidelity is measured by quantum state tomography to be above 90(2)% for any input polarization, which far exceeds the classical limit of 2 3. The process also constitutes a quantum non-destructive probe that detects and regenerates a photon without touching itspotentially undetermined -polarization.The power of quantum communication can be boosted by quantum memories [1,2,3,4,5,6,7,8,9,10,11] that can receive, store, and release a quantum state typically carried by a photon. The advantages memories offer, however, are often thwarted by photon losses [1,12,13,14]. Such unpredictable failure may be largely remedied by a heralding feature that announces photon arrival and successful storage without destroying or revealing the stored quantum state. Heralded storage may thus advance long-distance quantum communication [1], linear-optics quantum computing [15], or schemes aimed at breaking quantum encryption [16].Quantum state storage has been investigated in various systems [2,3,4,5,6,7,8,9,10]. Atomic-ensemble quantum memories have been pursued both for continuous variables of electromagnetic fields [17,18], and for quantized photonic excitations [3,4,6,7,8,10,11]. In an elegant experiment, Julsgaard et. al.[18] mapped the quadrature variables of a weak coherent field onto an atomic ensemble through a field measurement and subsequent feedback onto the ensemble. Other advancements towards a continuous-variable memory include the recent demonstration of storage and retrieval of squeezed vacuum [19,20].Much progress has been made in the storage and retrieval of individual photons. Early work demonstrated capture and release of single photons of fixed polarization using electromagnetically induced transparency [6,7], as well as their adiabatic transfer between two ensembles via an optical resonator [21]. Matsukevich and Kuzmich showed that two atomic ensembles can serve as a twolevel system whose state can be prepared by a projective measurement [4]. Recently, Choi et. al. mapped photonic entanglement created by a polarizing beamsplitter onto two ensembles, and later retrieved the photon [11], realizing unheralded, but relatively high-efficiency, polarization storage. In work by Chen et. al., a successful Bell measurement between two photons resulted in probabilistic teleportation of a photon polarization state onto two atomic ensembles [22]. This can be viewed as a partially heralded quantum memory, where a two-photon coincidence between two beams with Poissonian statistics sometimes, but not always, heralds a successful Bell measurement and teleportation [22].In this Letter, we demonstrate a system where a single photon announces polarization storage in the form of a single collective-spin excitation (magnon) that is shared between two spatially overlapped atomic ensembles. The heralded storage occurs rarely...

Partially Nondestructive Continuous Detection of Individual Traveling Optical Photons

“…The normalized cross-correlation function violates the Cauchy-Schwarz inequality, confirming the nonclassical character of the correlations. DOI: 10.1103/PhysRevLett.116.033602 Photons are unique carriers of quantum information that can be strongly interfaced with atoms for quantum state generation and processing [1][2][3][4][5][6][7][8][9]. Quantum state detection, a particular type of processing, is at the heart of quantum mechanics and has profound implications for quantum information technologies.…”

Coherent manipulation of spin-wave vector for polarization of photons in an atomic ensemble

“…Recently, the experimental studies on collective qubit memory used to achieve the atom-photon entanglement have had great progress. In these studies [7][8][9], two orthogonal [7] or two spatially distinct [8] spin waves, or two atomic ensembles shared a spin-wave excitation [9] are used to encode the long-time atomic qubit. The life time of qubit memory for optical lattice spin wave has reached to 3ms [7].…”

Many-atom–cavity QED system with homogeneous atom–cavity coupling

“…Topics studied include cavity-aided entanglement generation (spin squeezing) for quantum-enhanced metrology [3][4][5]; opto-mechanics with atoms, where collective motional degrees of freedom are coupled to cavity fields [6,7]; cavity-enhanced atomic quantum memories for quantum information processing [8]; and ultra-narrow-linewidth lasers using narrow-transition ultra-cold atoms as the gain medium for metrological purposes [9,10]. Important in many such systems is the inhomogeneity in the coupling strength between the participating atoms and the cavity field, which degrades the coherence of the interactions and complicates the dynamics and the analysis of the basic physics by obscuring the relevant system parameters.…”