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Quantum Memory for Light

Danish Quantum Optics Center University of Aarhus. QuanTOp. Quantum Memory for Light. Quantum memory for light: criteria. Memory must be able to store independently prepared states of light. The state of light must be mapped onto the memory with

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Quantum Memory for Light

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  1. Danish Quantum Optics Center University of Aarhus QuanTOp Quantum Memory for Light

  2. Quantum memory for light: criteria • Memory must be able to store independently prepared • states of light • The state of light must be mapped onto the memory with • the fidelity higher than the fidelity of the best • classical recording • The memory must be readable B. Julsgaard, J. Sherson, J. Fiurášek , I. Cirac, and E. S. Polzik Nature, 432, 482(2004); quant-ph/0410072.

  3. Quantum computing with linear operations Quantum buffer for light More efficient repeaters Quantum Key storage in quantum cryptography These criteria should be met for memory in:

  4. Mapping a Quantum State of Light onto Atomic Ensemble Spin Squeezed Atoms 1 > 2 > 0 > Experiment: Hald, Sørensen, Schori, EP PRL 83, 1319 (1999) Very inefficient lives only nseconds, but a nice first try… The beginning. Complete absorption Squeezed Light pulse Proposal: Kuzmich, Mølmer, EP PRL 79, 4782 (1997) Atoms

  5. …and feedback applied Strong driving Weak quantum Projection measurement on light can be made… or more atomic samples Dipole off-resonant interaction entangles light and atoms Our light-atoms interface - the basics Light pulse – consisting of two modes

  6. x,p Bell measurement Teleportation in the X,P representation

  7. Projection measurement X Today: another idea for (remote) state transfer and its experimental implementation for quantum memory for light See also work on quantum cloning: J. Fiurasek, N. Cerf, and E.S. Polzik, Phys.Rev.Lett.93, 180501 (2004)

  8. Implementation: light-to-matter state transfer - C squeeze atoms first No prior entanglement necessary = C Feedback magnetic coils Cesium atoms F≈80% F→100% B. Julsgaard, J. Sherson, J. Fiurášek , I. Cirac, and E. S. Polzik Nature, 432, 482(2004); quant-ph/0410072.

  9. e.-m. vacuum Classical benchmark fidelity for transfer of coherent states Atoms Best classical fidelity 50% K. Hammerer, M.M. Wolf, E.S. Polzik, J.I. Cirac, Phys. Rev. Lett. 94,150503 (2005),

  10. Preparation of the input state of light EOM Vacuum Input quantum field Coherent Squeezed Strong field A(t) Quantum field - X,P x Polarizing cube S1 P Polarization state X

  11. PL atoms Quantum memory – Step 1 - interaction Light rotates atomic spin – Stark shift XL Atomic spin rotates polarization of light – Faraday effect Output light Input light Entanglement

  12. PL XL c light out atoms Feedback to spin rotation Compare to the best classical recording Quantum memory – Step 2 - measurement + feedback Polarization measurement Fidelity – > 100% (82% without SS atoms)

  13. Experimental realization of quantum memory for light

  14. Encoding the quantum states in frequency sidebands

  15. Rotating frame spin Memory in atomic Zeeman coherences Cesium 4 3 2

  16. Memory in rotating spin states B B y z Atomic Quantum Noise 2,4 2,2 2,0 1,8 1,6 1,4 1,2 Atomic noise power [arb. units] 1,0 0,8 0,6 0,4 0,2 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 Atomic density [arb. units]

  17. Memory in rotating spin states - continued B B x z y Atomic Quantum Noise 2,4 2,2 2,0 1,8 1,6 1,4 1,2 Atomic noise power [arb. units] 1,0 0,8 0,6 0,4 0,2 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 Atomic density [arb. units]

  18. B B x z y

  19. Light Pin~ SYin Xin~ SZin p / 2 - rotation Stored state versus Input state: mean amplitudes X plane read write t output input Y plane Magnetic feedback

  20. Stored state: variances Absolute quantum/classical border 3.0 Perfect mapping Atoms <P2mem > Light <P2in >=1/2 <X2mem> <X2in> =1/2

  21. Experiment 0.68 Coherent states with 0 < n <4 Coherent states with 0 < n <8 0.66 F Experiment 0.64 0.64 0.62 0.62 Best classical mapping 0.58 0.58 0.56 0.56 Best classical mapping 0.54 Gain 0.65 0.7 0.75 0.8 0.85 0.9 0.82 0.84 0.86 0.88 0.9 Fidelity of quantum storage • State overlap averaged over • the set of input states

  22. Quantum memory lifetime

  23. Quantum Memory for Light demonstrated • Deterministic Atomic Quantum Memory proposed and • demonstrated for coherent states with <n> in • the range 0 to 10; lifetime=4msec • Fidelity up to 70%, markedly higher than best • classical mapping

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