Scavenging quantum information: Multiple observations of quantum systems
| Authors | |
|---|---|
| Year of publication | 2011 |
| Type | Article in Periodical |
| Magazine / Source | Physical Review A |
| MU Faculty or unit | |
| Citation | |
| Web | http://pra.aps.org/abstract/PRA/v84/i3/e032326 |
| Doi | http://dx.doi.org/10.1103/PhysRevA.84.032326 |
| Field | Theoretical physics |
| Keywords | Quantum information processing; quantum measurement |
| Description | Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system collapses into a postmeasurement state from which the same observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or can scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity when one or several qudits are available to carry information about the single-qudit state, and we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. |
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