Stephen D Bartlett et al 2009 New J. Phys. 11 063013 doi:10.1088/1367-2630/11/6/063013
Stephen D Bartlett1, Terry Rudolph2,3, Robert W Spekkens4 and Peter S Turner5
Show affiliationsTypical quantum communication schemes are such that to achieve perfect decoding the receiver must share a reference frame (RF) with the sender. Indeed, if the receiver only possesses a bounded-size quantum token of the sender's RF, then the decoding is imperfect, and we can describe this effect as a noisy quantum channel. We seek here to characterize the performance of such schemes, or equivalently, to determine the effective decoherence induced by having a bounded-size RF. We assume that the token is prepared in a special state that has particularly nice group-theoretic properties and that is near-optimal for transmitting information about the sender's frame. We present a decoding operation, which can be proven to be near-optimal in this case, and we demonstrate that there are two distinct ways of implementing it (corresponding to two distinct Kraus decompositions). In one, the receiver measures the orientation of the RF token and reorients the system appropriately. In the other, the receiver extracts the encoded information from the virtual subsystems that describe the relational degrees of freedom of the system and token. Finally, we provide explicit characterizations of these decoding schemes when the system is a single qubit and for three standard kinds of RF: a phase reference, a Cartesian frame (representing an orthogonal triad of spatial directions), and a reference direction (representing a single spatial direction).
03.67.Hk Quantum communication
03.67.Lx Quantum computation architectures and implementations
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
Issue 6 (June 2009)
Received 31 December 2008
Published 8 June 2009
Stephen D Bartlett et al 2009 New J. Phys. 11 063013
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