Principal Investigator: Professor Harald Weinfurter
The Project
Quantum memories and Interfaces: Single Trapped Atoms
The aim of this project is to develop a quantum interface between photonic qubits and a quantum processor based upon hyperfine states of a Rubidium atom confined within a dipole trap. The hyperfine structure of Rubidium-87 provides a suitable scheme for observation of entanglement between atomic and photonic states. This would allow state transfer between atomic and photonic qubits via quantum teleportation protocols.
The instantaneous dipole moment induced on an atom driven by a far off-resonance laser field results in an intensity dependent force upon the atom. For a large negative frequency detuning this dipole force pushes atoms towards regions of higher laser intensity, thus allowing confinement of atoms within a region of suitably intersecting laser beams.
In this implementation a single Rubidium atom, confined within a dipole trap of radius 3.5µm, acts as a quantum processor. Selective pumping prepares the trapped atom in an excited hyperfine state which can decay to three possible ground states with magnetic quantum numbers MF=-1,0 or +1 by spontaneously emitting a σ+, π or σ- polarised photon, respectively. Photons with σ-polarisation are detected in the same spatial mode and analysed to determine their polarisation while those with π-polarisation are ignored. Provided the emission processes are indistinguishable in all degrees of freedom other than polarisation, the atom-photon system will be in a maximally entangled state. Entanglement may be confirmed by suitable measurement of the atomic state after the spontaneous decay.
Initially this project will focus on observation of atomic-photonic entanglement in the system described [1] and efficient detection of atomic states. The system will provide insight into the critical parameters for quantum memory and should allow accurate testing of Bell’s inequality. Long term objectives include demonstration of entanglement over a reasonable distance and development of protocols for remote state preparation and Bell state measurement.
Quantum networks: Multiphoton Networks
The goal of this project is to demonstrate multipartite entanglement of various classes, and use it to improve quantum network performance.
Distribution of entangled states of light to particular locations is a key enabling technology for quantum information processing. Robust quantum networks will require several entangled particles, either directly for computation or for error correction to preserve a logical qubit or qudit.
Four-photon entangled cluster states will be demonstrated and used to implement quantum communication protocols, such as quantum secret sharing. In addition, generation of multipartite hyperentangled states – that is those entangled in more than one degree of freedom (polarization, frequency, direction etc.) – will be demonstrated.
Other QAP Activities
Researchers at LMU are also involved in other QAP projects. These are:
- Qudits and continuous variables with IMPERIAL
- Multi-particle and qudit entanglement purification and algorithms with IMPERIAL
- Testing small-scale quantum networks and devices with HPLB
- Quantum Channels with UG
- Terrestrial and satellite free-space quantum communication with OEAW
List of Publications
QAP
N. Kiesel, C. Schmid, U. Weber et al, Experimental Analysis of a Four-Qubit Photon Cluster State, Phys. Rev. Lett. 95 210502 (2005) quant-ph/0508128
N. Kiesel, C. Schmid, U. Weber et al, Linear Optics Controlled-Phase Gate Made Simple, Phys. Rev. Lett. 95 210505 (2005) quant-ph/0506269
J. Volz, M. Weber, D. Schlenk, W. Rosenfeld, J. Vrana, K. Saucke, C. Kurtsiefer and H. Weinfurter, Observation of Entanglement of a Single Photon with a Trapped Atom, Phys. Rev. Lett. 96 030404 (2006)
M. Weber, J. Volz, K. Saucke, C. Kurtsiefer, and H. Weinfurter, Analysis of a single-atom dipole trap, Phys. Rev. A 73 043406 (2006) quant-ph/0511232
W. Rosenfeld, S. Berner, J. Volz, M. Weber, and H. Weinfurter, Remote Preparation of an Atomic Quantum Memory, Phys. Rev. Lett. 98 050504 (2007)
S. Gaertner, C. Kurtsiefer, M. Bourennane et al, Experimental demonstration of four-party quantum secret sharing, Phys. Rev. Lett. 98 020503 (2007)
N. Kiesel, C. Schmid, G. Toth, E. Solano, and H. Weinfurter, Experimental Observation of Four-Photon Entangled Dicke State with High Fidelity, Phys. Rev. Lett. 98 063604 (2007) quant-ph/0606234
C. Schmid, N. Kiesel, W. Laskowski et al, The Entanglement of the Symmetric Four-photon Dicke State, NATO. Proceedings (2007)
C. Schmid, N. Kiesel, W. Wieczorek, and H. Weinfurter, The entanglement of the four-photon cluster state, accepted for publication in New. J. Phys.
C. Schmid, N. Kiesel, W. Wieczorek, R. Pohlner, and H. Weinfurter, Multiphoton entanglement engineering via projective measurements, Proc. SPIE 6780 67800E (2007)W. Wieczorek, N. Kiesel, C. Schmid, and H. Weinfurter, Efficient non-tomographic tools for the characterization of multipartite entanglement, Proceeding QCMC06 487 (2007)
S. Gaertner, M. Bourennane, C. Kurtsiefer et al, Experimental demonstration of a quantum protocol for Byzantine agreement and liar detection, Phys. Rev. Lett. 100 070504 (2008) arXiv:0710.0290
C. Schmid, N. Kiesel, W. Laskowski et al, Discriminating Multipartite Entangled States, Phys. Rev. Lett. 100 200407 (2008) arXiv:0804.3154
C. Schmid, N. Kiesel, W. Wieczorek,
H. Weinfurter, F. Mintert, and A. Buchleitner,
Experimental Direct Observation of Mixed State Entanglement,
Phys. Rev. Lett. 101 260505 (2008)
D. Richart,
Entanglement of Higher Dimensional Quantum States, Diplom thesis
(2008)
W. Wieczorek, C. Schmid, N. Kiesel et al, Experimental observation of an entire family of four-photon entangled states, Phys. Rev. Lett. 101 010503 (2008) arXiv:0806.1882
W. Rosenfeld, M. Weber, J. Volz, F. Henkel, M. Krug, A. Cabello, M. Zukowski, and H. Weinfurter, Towards a Loophole-Free Test of Bell's Inequality with Entangled Pairs of Neutral Atoms, Adv. Sci. Lett. 2 469 (2009) arXiv:0906.0703
G. Toth, W. Wieczorek, R. Krischek, N. Kiesel, P. Michelberger, and H. Weinfurter, Practical methods for witnessing genuine multi-qubit entanglement in the vicinity of symmetric states, New. J. Phys. 11 083002 (2009) arXiv:0903.3910
W. Wieczorek, Multi-Photon Entanglement: Experimental Observation, Characterization, and Application of up to Six-Photon Entangled States, PhD. thesis (2009)
W. Wieczorek, R. Krischek, N. Kiesel,
P. Michelberger, G. Toth, and H. Weinfurter,
Experimental Entanglement of a Six-Photon Symmetric Dicke State,
Phys. Rev. Lett. 103 020504 (2009)
arXiv:0903.2213
W. Wieczorek, N. Kiesel, C. Schmid, W. Laskowski, M. Zukowski, and H. Weinfurter, Multiphoton Interference as a Tool to Observe Families of Multiphoton Entangled States, IEEE. J. Sel. Topics Quantum Electronics 15 1704 (2009)
W. Wieczorek, N. Kiesel, C. Schmid, and H. Weinfurter, Multiqubit entanglement engineering via projective measurements, Phys. Rev. A 79 022311 (2009) arXiv:0901.4091
N. Kiesel, W. Wieczorek, S. Krins, T. Bastin, H. Weinfurter, and E. Solano, Operational multipartite entanglement classes for symmetric photonic qubit states, Phys. Rev. A 81 032316 (2010) arXiv:0911.5112
R. Krischek, W. Wieczorek, A. Ozawa et al, Ultraviolet enhancement cavity for ultrafast nonlinear optics and high-rate multiphoton entanglement experiments, Nature Phys. 4 170 (2010)
Related Work
J. Volz, Atom-Photon Entanglement, PhD. thesis (2006)
J. K. Pachos, W. Wieczorek, C. Schmid et al, Revealing anyonic statistics with multiphoton entanglement, submitted to Phys. Rev. Lett. arXiv:0710.0895v2
C. Schmid, A. P. Flitney, W. Wieczorek et al, Experimental implementation of a four-player quantum game, submitted to arXiv arXiv:0901.0063
R. Ursin et al, Space-QUEST: Experiments with quantum entanglement in space, accepted for publication in 59th International Astronautical Congress quant-ph/0806.0945