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
W. Rosenfeld, S. Berner, J. Volz, M. Weber, and H. Weinfurter, Remote Preparation of an Atomic Quantum Memory, Phys. Rev. Lett. 98 050504 (2007)
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)
R. Ursin et al, Space-QUEST: Experiments with quantum entanglement in space, accepted for publication in 59th International Astronautical Congress quant-ph/0806.0945
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
S. Gaertner, C. Kurtsiefer, M. Bourennane et al, Experimental demonstration of four-party quantum secret sharing, Phys. Rev. Lett. 98 020503 (2007) arXiv:0610112v1
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, N. Kiesel, W. Laskowski et al, Discriminating Multipartite Entangled States, Phys. Rev. Lett. 100 200407 (2008) arXiv:0804.3154
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
Related Work
J. Volz, Atom-Photon Entanglement, PhD. thesis (2006)
N. Kiesel, C. Schmid and U. Weber, Geza Toth, Otfried Gühne, Rupert Ursin and Harald Weinfurter, Experimental Analysis of a Four-Qubit Photon Cluster State, Phys. Rev. Lett. 95 210502 (2005) quant-ph/0508128
N. Kiesel, C. Schmid and U. Weber, Rupert Ursin and Harald Weinfurter, Linear Optics Controlled-Phase Gate Made Simple, Phys. Rev. Lett. 95 210505 (2005) quant-ph/0506269
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