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arXiv:quant-ph/0703059 · Physical Review Letters

Quantum Communication without Alignment using Multiple-Qubit Single-Photon States

Leandro Aolita, Stephen Patrick Walborn

Published Mar 6, 2007• 117 citations
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Abstract

We propose a scheme for encoding logical qubits in a subspace protected against collective rotations around the propagation axis using the polarization and transverse spatial degrees of freedom of single photons. This encoding allows for quantum key distribution without the need of a shared reference frame. We present methods to generate entangled states of two logical qubits using present day down-conversion sources and linear optics, and show that the application of these entangled logical states to quantum information schemes allows for alignment-free tests of Bell's inequalities, quantum dense coding, and quantum teleportation.

DOI
10.1103/physrevlett.98.100501

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We propose an alignment-free photonic qubit transmission scheme and apply it in quantum key distribution schemes, in which the authorized parties do not have to calibrate their Cartesian reference frames in advance. The polarization states are labeled by time, and the receiver can obtain the original state in his own coordinate by postselecting a determinate time of arrival. The scheme does not resort to decoherence-free subspace based on multiple photon states, and it can be implemented with only passive linear optics, which make it efficient and practical with current technology. We demonstrate its application in quantum key distributions, and the scheme should find applications in long-distance quantum communication without frame alignment.