Quantum communication using a bounded-size quantum reference frame
Quantum communication using a bounded-size quantum reference frame
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DOI：
10.1088/1367-2630/11/6/063013
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发表时间：
2009-06-08
影响因子：
3.3
通讯作者：
Turner, Peter S.
中科院分区：
文献类型：
--
作者：
Bartlett, Stephen D.;Rudolph, Terry;Turner, Peter S.
典型的量子通信方案是这样的，为了实现完美的解码，接收器必须与发送器共享参考系（RF）。事实上，如果接收方只拥有发送方RF的有限大小的量子令牌，那么解码是不完美的，我们可以将这种效应描述为噪声量子信道。我们在这里寻求这样的计划，或等效的性能特征，以确定有效的退相干诱导有界尺寸的RF。我们假设令牌是在一个特殊的状态下准备的，该状态具有特别好的群论性质，并且对于发送方帧的传输信息来说是接近最优的。我们提出了一种解码操作，在这种情况下可以证明该操作是接近最佳的，并且我们证明了有两种不同的方法来实现它（对应于两种不同的克劳斯分解）。在一种情况下，接收器测量RF令牌的取向并适当地重新定向系统。在另一种情况下，接收器从虚拟子系统中提取描述系统和令牌的关系自由度的编码信息。最后，我们提供了明确的表征这些解码方案时，系统是一个单一的量子比特和三种标准的RF：相位参考，笛卡尔坐标系（代表一个正交的空间方向），和参考方向（代表一个单一的空间方向）。
Typical 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).