Quantum information with pulsed photons

Tracy E. Northup, R. Blatt

Sergey A. Moiseev, Wolfgang Tittel

We study quantum compression and decompression of light pulses that carry quantum information using a photon-echo quantum memory technique with controllable inhomogeneous broadening of an isolated atomic absorption line. We investigate media with differently broadened absorption profiles, transverse and longitudinal, finding that the recall efficiency can be as large as unity and that the quantum information encoded into the photonic qubits can remain unperturbed. Our results provide insight into reversible light-atom interaction and are interesting in view of future quantum communication networks, where pulse compression and decompression may play an important role in increasing the qubit rate or in mapping quantum information from photonic carriers with large optical bandwidth into atomic memories with smaller bandwidth.

Stasja Stanisic

Li Yongfang

Using the method of the Bloch vectors,the physics mechanism of the photon echo is analyzed with both the dressed state and quantum interference theory,and the physics picture for the interaction between light and atoms is given in detail.The dynamic process for the quantum information storage and that of the recall with the photon echo is discussed under adiabatic condition.The results show that the photon information is stored in the medium during the first pulse,and when v and w of the Bloch vectors are inversed during the second pulse,the information reappears as the photon echo.The process of the photon echo is virtually the process of photon information storage and recall.

Maria Maffei, Bruno O. Goes, Stephen C. Wein +3 more

Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed at coherently transferring quantum information between spin qubits and propagating pulses of polarized light. We study the potential of a SPI for quantum non demolition (QND) measurements of a spin state. After being initialized and scattered by the SPI, the state of a light pulse depends on the spin state. It thus plays the role of a pointer state, information being encoded in the light's temporal and polarization degrees of freedom. Building on the fully Hamiltonian resolution of the spin-light dynamics, we show that quantum superpositions of zero and single photon states outperform coherent pulses of light, producing pointer states which are more distinguishable with the same photon budget. The energetic advantage provided by quantum pulses over coherent ones is maintained when information on the spin state is extracted at the classical level by performing projective measurements on the light pulses. The proposed schemes are robust against imperfections in state of the art semi-conducting devices.

Dik Bouwmeester, John C. Howell, Antía Lamas Linares