Speaker
Description
Quantum optics allows implementing cryptographic protocols that are verifiably immune against any conceivable attack. Standard telecommunication components allow for an efficient implementation of quantum communication using continuous-variables (CV) of light. At MPL, we routinely implement CV quantum communication based on phase-shift keying of coherent states in combination with homodyne detection [1,2].
Existing fiber infrastructure is not suitable for long-haul links between metropolitan networks since classical telecom repeaters cannot relay quantum states. A space borne Laser Communication Terminal (LCT), however, would be capable to relay quantum key distribution (QKD) between a large number of hubs on ground. To this end, we demonstrated quantum-limited measurements of signals from the Alphasat satellite in geostationary Earth orbit (GEO) [3]. Our results underpin the feasibility of satellite quantum communication based on existing technology.
On the fundamental research side, the large gravitational potential difference between GEO and ground offers an ideal testbed to investigate gravitational effects on quantum states.
Our measurements from the Alphasat satellite showed that atmospheric noise can be overcome and that merely the huge diffraction losses pose challenges for the detection of quantum properties such as quantum squeezing.
For homodyne detectors in classical telecommunication, the precise measurement value of the continuous quadrature observable is of minor significance. The signals in BPSK encoding, for instance, are discriminated based on the sign of the measurement outcome, such that the signals are often projected onto their sign bit thereby precluding the access to the continuous quadrature spectrum. We investigate the implications of this extremal discretization with regard to the detection of quantum squeezing and find that it can still be witnessed efficiently [4].
[1] B. Heim et al., arXiv:1402.6290v2[quant-ph]
“Atmospheric continuous-variable quantum communication”
New Journal of Physics 16, 113018 (2014)
[2] C. Peuntinger et al., arXiv:1406.1321v1[quant-ph]
“Distribution of Squeezed States Through an Atmospheric Channel”
Phys. Rev. Lett. 113, 060502 (2014)
[3] K. Günthner et al., arXiv:1608.03511v2[quant-ph] (2016)
“Quantum-limited measurements of optical signals from a geostationary satellite”
(accepted in Optica)
[4] C. R. Müller et al.
„ Witnessing Quantum Squeezing via Binary Homodyne Detection“
(in preparation)
| Topic: | Mini-workshop: Continuous Variables and Relativistic Quantum Information |
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