Cryptography Reference
In-Depth Information
using a concatenated code as described by KLM [1]. It may also be possible to
reduce the requirements on the number of ancilla and the detector efficiency
by using a hybrid approach, such as the Zeno gates [35] that were briefly
mentioned above.
6.6 Summary
In summary, we have reviewed some of the challenges faced by quantum
communications systems, both past and present. Earlier difficulties associ-
ated with changes in the state of polarization and sensitivities to interferom-
eter phase drift have been largely overcome. Although free-space systems
will probably be used for special applications, their bandwidth is limited,
and quantum repeaters will probably be required in order to achieve the de-
sired bandwidth and operating range. We have demonstrated several kinds
of quantum logic gates [6-8], along with a prototype source of single photons
[9] and a quantum memory device [4]. As shown by the group at JPL [5], these
techniques can be combined with a four-qubit code to correct for the effects
of photon loss and to implement a quantum repeater system. Further work
will be required in order to reduce the failure rate of linear optics quantum
logic gates, possibly including the development of hybrid approaches such
as Zeno gates [35].
Acknowledgments
This work was supported by the Army Research Office and Independent
Research and Development (IR&D) funds.
References
1. E. Knill, R. Laflamme, and G.J. Milburn,
Nature
, 409, 46, 2001.
2. J.D. Franson, M.M. Donegan, M.J. Fitch, B.C. Jacobs, and T.B. Pittman, Phys.
Rev. Lett., 89, 137901, 2002.
3. J.D. Franson and T.B. Pittman, Proceedings of the fundamental problems in
quantum theory workshop, D. Lust and W. Schleich, eds., Fortschritte der
Physik, 46, 697-705, 1998.
4. T.B. Pittman and J.D. Franson, Phys. Rev. A, 66, 062302, 2002.
5. R.M. Gingrich, P. Kok, H. Lee, F. Vatan, and J.P. Dowling, Phys. Rev. Lett., 91,
217901, 2003.
6. T.B. Pittman, B.C. Jacobs, and J.D. Franson, Phys. Rev. A, 64, 062311, 2001.
7. T.B. Pittman, B.C. Jacobs, and J.D. Franson, Phys. Rev. Lett., 88, 257902, 2002.
8. T.B. Pittman, M.J. Fitch, B.C. Jacobs, and J.D. Franson, Phys. Rev. A, 68, 032316,
2003.
9. T.B. Pittman, B.C. Jacobs, and J D. Franson, Phys. Rev. A, 66, 042303, 2002.
10. C.H. Bennett, F. Bessette, G. Brassard, L. Salvail, and J. Smolin, J. Cryptology,
5, 3, 1992.
11. J.D. Franson and H. Ilves, Appl. Optics, 33, 2949-2954, 1994.
