WP1.4: Single trapped Atoms

1. WP1.4: Single trapped Atoms • General Objectives • Generate entanglement between quantum memory • and single photon over large distance (several 100 m). • Perform “read/write” operations via • quantum teleportation protocols. • Generate atom-atom entanglement over • large distances (quantum repeater). • Loophole-free test of Bell’s inequality M 1.4.5 Establish stable optical fiber link for long-distance applications (M27) M 1.4.6: Observation of single atoms in second mobile trap (M36) D 1.4.3:Observation of long-distance atom-photon entanglement (M30)

2. WP1.4: Single trapped Atoms atomic basis atomic basis D 1.4.3:Observation of long-distance atom-photon entanglement M 1.4.5:Establish stable optical fiber-link for long-distance applications • atom-photon correlations over 300 m W. Rosenfeld et al., arXiv:0808.3538v1 [quant-ph]

3. WP1.4: Single trapped Atoms M 1.4.6:Observation of single atoms in second mobile dipole trap • new setup Improved photon detection efficiency = 0.21 % Planning for period 4 M 1.4.7: Theoretical calculation of expected atom-atom entanglement fidelity (M 39) M 1.4.8: Observation of atom-photon entanglement in second mobile dipole trap (M 42) D 1.4.4: Observation of quantum interference of photon pairs from two trapped atoms (M 48)

4. WP1.5: Room-T Atomic Vapour QUANTOP • Objective • A Memory for a quantum state of light in an atomic ensemble of Cs atoms with a fidelity of up to 70%, had previously been demonstrated. The goal in this WP is to investigate further approaches to the memory, all based on gas in glass cells. • M1.5.6 Implementation of and conclusion on storage of squeezed and entangled light states in thermal atomic ensembles – partly achieved: • storage of displaced, squeezed light states • two-mode storage of displaced, squeezed light states  identical to storage of two entangled states • storage of one part of entangled beams • D1.5.3 Application of improved fidelity storage to non-classical light states – partly achieved: • storage of non-classical light states (displaced, squeezed states) improved fidelity by technical means: • flat-top beam profile • digital feedback • improved detection efficiency • improved fidelity by optimized temporal mode functions • improved storage fidelity by atomic squeezing • New milestones (month 42 and 48) • M1.5.7 protocols for atomic - atomic state teleportation • M1.5.8 technical and physical limitations to performance of atomic - atomic state teleportation • New deliverable (month 48) • D1.5.4 Conclusion on performance of light-to-atoms and atoms-to- atoms Hi-Fi state transfer

5. ξ-1 QUANTOP Best classical fidelity vs degree ofsqueezing for arbitrary displaced states ξ-1 D1.5.3 Classical benchmark memory fidelity derived for a new class of states M.Owari, M.Plenio, E.Polzik, A.Serafini, M.M.Wolf, arXiv:0808:2260, accepted by NJP. storage fidelity classical limit η – added noise in vacuum units, ξ-1 – squeezed variance

6. QUANTOP 0 dB 5 dB Classical benchmark D1.5.3 Preliminary results: deterministic quantum memory for displaced squeezed states with fidelity better than classical benchmark light state tomography atomic state tomography preliminary data

7. WP1.5: Room-T Atomic Vapour Herald Achievements • Set up components for and achieved efficient optical pumping in Cesium for state preparation • Tested repeatability of optical phonon coherence measurement in bulk diamond • Developed a quantum-optical interpretation of optical phonon excitations [1,2] • Enhanced a paper on multimode storage using the off-resonant Raman scheme; accepted for publication [3] • Characterized the Zeeman splitting inhomogeneity and Schottky-contact charging of quantum dot samples |Ψ>=|01>±|10> Pump Read-out Schematic of spatial entanglement of optical phonon excitations in bulk diamond • Proposed Objectives • Characterize fidelity of deterministic storage and retrieval of broadband weak coherent states using an ancillary control field in Cesium vapor (# 9) • Characterize and implement heralded single-phonon excitation of bulk diamond (# 12) • Implement spatial entanglement of optical phonon excitations in bulk diamond (see diagram) • Develop quantum dot samples with waveguides for an ensemble quantum memory [1] F. Waldermann et al., submitted to PRB. [2] F. Waldermann et al., Diam. Relat. Mater. 16, 1887-1895 (2007). [3] J. Nunn et al., Phys. Rev. A 78, 033806 (2008).

8. WP1.6: Cold Atoms QUANTOP • Objective • The general goal of this WP is to develop interfaces between light and cold atoms. In addition to a memory of single photon qubits, we want to demonstrate spin squeezing at Cs clock transition based on atom light interaction with the ultimate goal to improve the sensitivity of atom clocks. D1.6.3: Investigation of quantum properties of light coupled to the Rb BEC(due: month 24) . Partly achieved, to be continued D1.6.4: Application of atomic state tomography to excitations in quantum memories(due: month 36) . Partly achieved, to be continued M1.6.6: Assessment of decoherence rates for Rubidium and Cesium atomic samples trapped in state insensitive potentials. (due: month 30) . Partly achieved, to be continued M1.6.7: Assessment of conditional state preparation in the few excitation regime for trapped Cesium and Rubidium atomic samples; Choice of the target system (due: month 33). Partly achieved M1.6.8: Implementation of atomic state tomography on the chosen target system(due: month 36) . Partly achieved ( to be continued)

9. QUANTOP D1.6.4 Spin Squeezing and Entanglement in the Cs Clock – tomography of the nonclassical atomic state 3.3 dB of spectroscopically relevant pseudo-spin squeezing (projection noise corrected for decoherence from probing)

10. ALL SP1 WP1.7: Comparison • Objective • The objective of this WP is to compare, evaluate and analyse the different approaches to quantum memory for applications in quantum communication and computation. • M1.7.4: Assessment of status of quantum memory implementation (M36) • D1.7.3: Updated results on the comparison, evaluation and analysis of the different approaches to quantum memory for applications in quantum communication and computation (M36) Approaches to Quantum Memories 08 (Copenhagen: 10 - 11 July) Approaches to Quantum Memories 07 (Stuttgart: 21 - 22 June) Approaches to Quantum Memories 06 (Geneva: 29 - 30 June) • Goals: • Develop a common means of characterising and comparing the different quantum systems. • Developing collaborations • Structuring the Community • Revised vision! • Comparison table

11. ALL SP1 Copenhagen Comparison

12. ALL SP1 Copenhagen Comparison Entanglemt. with light Band width MM capacity Storage Time Efficiency Write-in Retrieval Measure ment Potential Applications Approach Fidelity Dim. 1 ms 10 MHz hin hout~ 0.01 4 not yet SPS, QRep LOC4 retrieval Yes with PDC 0.97 ~1 high RE AFC 30 s high cond. 1GHz 10 MHz not yet SPS, QRep LOC4 not yet not yet high RE CRIB ~1 retrieval moderate not yet Yes with PDC 30 s 100 MHz not yet ? low ? ? QRep, SPS ? NV with cavity low ~1 not yet ~0.2 ~0.2 not yet QD SPS low >GHz low retrieval not yet ~1 ~1 yes 1 ms 150 ms Single atoms Free space low with cavity low 6 MHz Write 0.94 cond Read 0.9 uncond low LHF, QRep h=1 done! ~1 >ms not yet 4 ms kHz Write 0.7 (uncond.) Msmt 0.6 LOC4, Prec.msmt. Room-temp. gas low h=1 high 1 done! ~1 200 ms 100 kHz not yet 1 MHz not yet not yet not yet Prec.msmt., LOC4, QRep moderate (spatial) Write not yet Read 0.75? h=1 high Cold gas ~1 yes 100 ms ~1 0.5 GHz not yet not yet not yet not yet Raman gas diamond not yet SPS, QRep moderate high retrieval not yet ~1 ~1 GHz Cs THz diam 1 ms Cs 10 ps diam yes