Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session Q5: Quantum Cryptography and Communication |
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Chair: G. Weihs, University of Waterloo Room: TELUS Convention Centre Macleod A3-A4 |
Friday, June 8, 2007 1:30PM - 1:42PM |
Q5.00001: Experimental techniques to enhance the performance of quantum key distribution systems Yi Zhao, Bing Qi, Xiongfeng Ma, Hoi-Kwong Lo Practical quantum key distribution (QKD) system has many imperfections, causing several security concerns. Nonetheless, people have proven the security of imperfect practical QKD systems. There are several approaches to enhance the performance of practical QKD system. A famous one is the decoy method, which can dramatically improve the efficiency of QKD (i.e., higher key rate, longer transmission distance) without jeopardizing the security. Another one is the phase randomization, which can improve the security of the QKD system (by making it closer to theoretical assumptions) without reducing the efficiency. Here, we report the \emph{first} experimental implementations of the decoy method\footnote{Y. Zhao \emph{et. al.}, Phys. Rev. Lett., \textbf{96}, 070502 (2006); Y. Zhao \emph{et. al.}, in \emph{Proceedings of IEEE ISIT} (IEEE, 2006) pp. 2094-2098.} and the active phase randomization\footnote{Y. Zhao, B. Qi, and H. -K. Lo, Appl. Phys. Lett., \textbf{90}, 044106 (2007).}. We implemented two decoy state QKD protocols: the one-decoy protocol over 15km telecom fiber, and the weak+vacuum protocol over 60km telecom fiber. We also implemented the active phase randomization over 5km. The experimental results confirmed the phase randomization and that the efficiency of QKD system was not reduced. [Preview Abstract] |
Friday, June 8, 2007 1:42PM - 1:54PM |
Q5.00002: Quantum key distribution with entangled sources Xiongfeng Ma, Chi-Hang Fred Fung, Hoi-Kwong Lo We propose a model and a post-processing protocol for quantum key distribution (QKD) with entangled photons from a parametric down-conversion (PDC) source. We also investigate the entanglement PDC QKD with two-way classical communications. We find that the recurrence scheme increases the key rate and Gottesman-Lo protocol helps tolerate higher channel losses. By simulating a real QKD setup, we compare three implementations --- entanglement PDC QKD, triggering PDC QKD and coherent state QKD. The simulation result suggests that the entanglement PDC QKD can tolerate higher channel losses than the coherent state QKD. On the other hand, the coherent state QKD with decoy states is able to achieve highest key rate in the low and medium-loss regime. By applying Gottesman-Lo two-way post-processing protocol, the entanglement PDC QKD can tolerate up to 70dB combined channel losses (35dB for each channel) provided that the PDC source is placed in between Alice and Bob rather than at Alice's side. Since a 35dB channel loss is similar to the estimated loss in a satellite to ground quantum transmission, our result is in agreement with the suggestion in the literature that secure QKD between two ground locations via an {\it untrusted} satellite with an entanglement-based PDC source appears to be technologically feasible. [Preview Abstract] |
Friday, June 8, 2007 1:54PM - 2:06PM |
Q5.00003: Eavesdropping of quantum communication from a non-inertial frame. Kamil Bradler We introduce a relativistic version of quantum encryption protocol by considering two inertial observers who wish to securely transmit quantum information encoded in a free scalar quantum field state forming Minkowski particles. In a non-relativistic setting a certain amount of shared classical resources is necessary to perfectly encrypt the state. We show that in the case of a uniformly accelerated eavesdropper the communicating parties need to share (asymptotically in the limit of infinite acceleration) just half of the classical resources. [Preview Abstract] |
Friday, June 8, 2007 2:06PM - 2:18PM |
Q5.00004: Towards Hybrid Quantum Communication Networks Wolfgang Tittel, Olivier Alibart, Pascal Baldi, Nicolas Gisin, Matthaeus Halder, Ivan Marcikic, Hugues De Riedmatten, Sebastien Tanzilli, Hugo Zbinden The last years have seen a remarkable advance of experimental realizations of applications of quantum communication. The most important example is quantum cryptography that is now at the verge of becoming an industrial application. One of the future challenges to make this technology widely available is the integration of point-to-point links into networks that may consist of hybrid quantum communication channels with fibre optic and free-space links. I will report on experiments that allow transferring quantum information between photons at different wavelengths, as required for different quantum channels, either based on quantum teleportation [1], or on parametric up-conversion in a non-linear crystal [2]. [1] I. Marcikic, H. de Riedmatten, W. Tittel, H. Zbinden, N. Gisin, Nature 421, 509 (2003). [2] S. Tanzilli, W. Tittel, M. Halder, O. Alibart, P. Baldi, N. Gisin, H. Zbinden, Nature 437, 116 (2005). [Preview Abstract] |
Friday, June 8, 2007 2:18PM - 2:30PM |
Q5.00005: Experimental Raman adiabatic transfer of optical states in rubidium J\"urgen Appel, Eden Figueroa, Frank Vewinger, Karl-Peter Marzlin, Alexander Lvovsky An essential element of a quantum optical communication network is a tool for transferring and/or distributing quantum information between optical modes (possibly of different frequencies) in a loss- and decoherence-free fashion. We present a theory [1] and an experimental demonstration [2] of a protocol for routing and frequency conversion of optical quantum information via electromagnetically-induced transparency in an atomic system with multiple excited levels. Transfer of optical states between different signal modes is implemented by adiabatically changing the control fields. The proof-of-principle experiment is performed using the hyperfine levels of the rubidium D1 line. [1] F. Vewinger, J. Appel, E. Figueroa, A. I. Lvovsky, quant-ph/0611181 [2] J. Appel, K.-P. Marzlin, A. I. Lvovsky, Phys. Rev. A \textbf{73}, 013804 (2006) [Preview Abstract] |
Friday, June 8, 2007 2:30PM - 2:42PM |
Q5.00006: Hybrid Entanglement for Optical Quantum Networks F\'elix Bussi\`eres, Nicolas Godbout, Wolfgang Tittel A global optical quantum communication network will have to operate with different encodings of quantum information (QI) depending on the medium in which the photons are carried. Polarization qubits in the visible spectrum are well suited for free-space transmission due to the absence of birefringence in the air, whereas time-bin qubits at telecom wavelengths are more suited for optical fiber transmission due to their resistance to polarization mode dispersion. We present a scheme to generate hybrid photonic entanglement defined as entanglement between different encodings of QI using light. In this specific case we consider a time-bin photon at 1550 nm entangled with a polarization photon at 805 nm and we report on our progress towards creating such a source using parametric down-conversion in bulk crystals. We also show how to teleport a polarization qubit to a time-bin qubit using this type of entanglement. Finally, we discuss how this allows QI to be distributed over optical quantum networks interfacing free-space and optical fiber links hence increasing the versatility of such networks. [Preview Abstract] |
Friday, June 8, 2007 2:42PM - 2:54PM |
Q5.00007: Multiplexed Memory-Insensitive Quantum Repeaters Odell Collins, Stewart Jenkins, T.A. Brian Kennedy, Alex Kuzmich Long-distance quantum communication via distant pairs of entangled quantum bits (qubits) is the first step towards secure message transmission and distributed quantum computing. To date, the most promising proposals require quantum repeaters to mitigate the exponential decrease in communication rate due to optical fiber losses. However, these are exquisitely sensitive to the lifetimes of their memory elements. We propose a multiplexing of quantum nodes that should enable the construction of quantum networks that are largely insensitive to the coherence times of the quantum memory elements. [Preview Abstract] |
Friday, June 8, 2007 2:54PM - 3:06PM |
Q5.00008: Towards Quantum Memory Wolfgang Tittel, Mikael Afzelius, Nicolas Gisin, Sara Hastings-Simon, Matthias Staudt The last years have seen a remarkable advance of quantum cryptography, which promises information-theoretic secure communication. A remaining challenge concerns the increase of the transmission distance beyond its current limit of 100 km. This requires the development of a quantum repeater, which relies on the possibility to store and recall photons in unknown quantum states. An original protocol for quantum memory is based on controlled reversible inhomogeneous broadening (CRIB) of a single atomic absorption line [1]. We will present experimental investigations of coherence times of Erbium doped fibres and crystalline waveguides [2], and the possibility to implement a controlled broadening by means of the linear dc-Stark effect [3]. The new findings demonstrate the potential of Erbium doped silicate fibers for CRIB based quantum state storage. [1] B. Kraus et al, Phys. Rev. A 73, 020302 (2006). [2] M.U. Staudt et al, Opt. Comm. 266, 720 (2006). [3] S.R. Hastings-Simon et al, Opt. Comm. 266, 716 (2006). [Preview Abstract] |
Friday, June 8, 2007 3:06PM - 3:18PM |
Q5.00009: Remote Preparation of an Atomic Quantum Memory M. Weber, W. Rosenfeld, J. Volz, S. Berner, H. Weinfurter Storage and distribution of quantum information are key elements of quantum information processing and quantum communication. Here, using atom-photon entanglement as the main physical resource [1], we experimentally demonstrate the preparation of a distant atomic quantum memory. Applying a quantum teleportation protocol on a locally prepared state of a photonic qubit, we realized this so-called remote state preparation on a single, optically trapped Rb87 atom. We evaluated the performance of this scheme by the full tomography of the prepared atomic state, reaching an average fidelity of 0.82 [2]. The principles enabling the successful remote state preparation now also can be applied to further quantum communication protocols, e.g. the quantum teleportation from light to matter and last but not least the quantum repeater [3]. \newline \newline [1] J. Volz, M. Weber et al., Phys. Rev. Lett. {\bf 96}, 030404 (2006). \newline [2] W. Rosenfeld, S. Berner, J. Volz, M. Weber, and H. Weinfurter, Phys. Rev. Lett. {\bf 98}, (2007). \newline [3] H.-J. Briegel et al., Phys. Rev. Lett. {\bf 81}, 5932 (1998). [Preview Abstract] |
Friday, June 8, 2007 3:18PM - 3:30PM |
Q5.00010: Dual Species Matter Qubit Entangled with Light S.-Y. Lan, S.D. Jenkins, T. Chaneliere, D.N. Matsukevich, C.J. Campbell, R. Zhao, T.A.B. Kennedy, A. Kuzmich We propose and demonstrate an atomic qubit based on a cold $^{85}$Rb-$^{87}$Rb isotopic mixture, entangled with a frequency-encoded optical qubit. The interface of an atomic qubit with a single spatial light mode, and the ability to independently address the two atomic qubit states, should provide the basic element of an interferometrically robust quantum network. [Preview Abstract] |
Friday, June 8, 2007 3:30PM - 3:42PM |
Q5.00011: Quantum interference of two photons emitted by two trapped Yb ions Kelly C. Younge, David L. Moehring, Steven Olmschenk, Dzmitry Matsukevich, Peter Maunz, Martin J. Madsen, Luming Duan, Chris Monroe Distant, entangled qubits represent a universal resource for quantum communication protocols and distributed quantum computing. One method to entangle two distant particles involves detecting a single photon from each particle after the photons have interfered. We demonstrate this two-photon quantum interference by using an ultrafast laser to excite two ytterbium ions trapped in spatially separated rf Paul traps. The emitted photons are transmitted through optical fibers to achieve high, stable mode overlap on a beam splitter. Two-photon interference, along with the excellent state preparation and detection available in trapped ion systems, should allow the two ions to be entangled without involving their motion. Such a quantum link can be used as a fundamental resource for large-scale quantum networks and scalable quantum computers. [Preview Abstract] |
Friday, June 8, 2007 3:42PM - 3:54PM |
Q5.00012: Quantum Interference of Electromagnetic Fields from Remote Quantum Memories R. Zhao, T. Chaneliere, D.N. Matsukevich, S.D. Jenkins, S.-Y. Lan, T.A.B. Kennedy, A. Kuzmich We observe quantum, Hong-Ou-Mandel, interference of fields produced by two remote atomic memories. High-visibility interference is obtained by utilizing the finite atomic memory time in four-photon delayed coincidence measurements. Interference of fields from remote atomic memories is a crucial element in protocols for scalable generation of multi-node remote qubit entanglement. [Preview Abstract] |
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