01126nas a2200169 4500008004100000022001400041245008700055210006900142260003900211300001100250490000700261520057500268100001700843700001700860700002400877856005500901 2004 eng d a1050-294700aEntanglement-assisted alignment of reference frames using a dense covariant coding0 aEntanglementassisted alignment of reference frames using a dense bAmerican Physical Societyc05/2004 a0503030 v693 aWe present a procedure inspired by dense coding, which enables a highly efficient transmission of information of a continuous nature. The procedure requires the sender and the recipient to share a maximally entangled state. We deal with the concrete problem of aligning reference frames or trihedra by means of a quantum system. We find the optimal covariant measurement and compute the corresponding average error, which has a remarkably simple close form. The connection of this procedure with that of estimating unitary transformations on qubits is briefly discussed.1 aBagan, Emili1 aBaig, Marià1 aMuñoz-Tapia, Ramon uhttp://link.aps.org/doi/10.1103/PhysRevA.69.050303