Quantum Atomic Clock Synchronization Based on Shared Prior Entanglement
Richard Jozsa2,DanielS.Abrams1, Jonathan P. Dowling1, and Colin P. Williams1 1 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109-8099. 2 Dept. of Computer Science, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK. (Received: May 3, 2000)
System of Units (SI), the unit of time is defined as the We demonstrate that two spatially separated parties (Al- second, which is the duration of exactly 9,192,631,770 ice and Bob) can utilize shared prior quantum entanglement, periods of oscillation corresponding to the hyperfine (ra- and classical communications, to establish a synchronized 133 pair of atomic clocks. In contrast to classical synchroniza- dio) transition frequency for the ground-state of the Cs atom [5]. The fact that this frequency is identical for all tion schemes, the accuracy of our protocol is independent of 133 Alice or Bob’s knowledge of their relative locations or of the Cs atoms, which are sufficiently isolated from the en- 133 properties of the intervening medium. vironment, allows anyone to establish a Cs time stan- PACS: 03.67.-a, 03.67.Hk, 06.30.Ft, 95.55.Sh dard of comparable accuracy. In general, any set of identical qubits may be used as In the Special Theory of Relativity, there are two meth- the time standard in a temporal interferometer, which ods for synchronizing a pair of spatially separated clocks, employs the Ramsey method of separated oscillatory A and B, which are at rest in a common inertial frame. fields [6]. In the language of quantum information the- The usual procedure is Einstein Synchronization (ES), ory this Ramsey interferometer corresponds to a sim- which involves an operational line-of-sight exchange of ple quantum circuit with just two gates, acting on one light pulses between two observers, say Alice and Bob, qubit. Specifically, let us suppose that the qubit has who are co-located with their clocks A and B, respec- energy eigenstates |0i and |1i with energy eigenvalues tively [1]. A less commonly used Clock Synchronization E0