Quantum Stopwatch: How To Store Time Information in a Quantum Memory

R. Sala Mayato, Daniel Alonso, I. L. Egusquiza

Yuxiang Yang, Giulio Chiribella, Masahito Hayashi

Atomic clocks are our most accurate indicators of time. Their applications range from GPS systems to synchronization of electronics, astronomical observations, and tests of fundamental physics. Here we propose a protocol that combines an atomic clock with a quantum memory, realizing a stopwatch that can be paused and resumed on demand. Taking advantage of the quantum memory, the stopwatch can measure the total time elapsed in a sequence of time intervals with the ultimate precision allowed by quantum mechanics, outperforming stopwatches that use only classical memories. The working principle of the quantum stopwatch is a new type of information compression,tailored to store the state of the quantum clock into a quantum memory of exponentially smaller size. Our protocol can be used to generate quantum states with Heisenberg limited sensitivity and to efficiently synchronize clocks in quantum communication networks.

Yuxiang Yang, Giulio Chiribella, Masahito Hayashi

Quantum mechanics imposes a fundamental trade-off between the accuracy of time measurements and the size of the systems used as clocks. When the measurements of different time intervals are combined, the errors due to the finite clock size accumulate, resulting in an overall inaccuracy that grows with the complexity of the set-up. Here, we introduce a method that, in principle, eludes the accumulation of errors by coherently transferring information from a quantum clock to a quantum memory of the smallest possible size. Our method could be used to measure the total duration of a sequence of events with enhanced accuracy, and to reduce the amount of quantum communication needed to stabilize clocks in a quantum network.

R. Sala Mayato, Daniel Alonso, I. L. Egusquiza

Tavshabad Kaur, Maninder Kaur, Arvind +1 more

We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration is comprised of an optomechanical system with additional Kerr nonlinearity in the optical mode and an anharmonic mechanical oscillator with quadratic nonlinearity. Time degradation is monitored, both in terms of loss of coherence, which is analyzed with the help of Wigner functions, as well as in terms of loss of amplitude of the original state, studied as a function of time. While our time trajectories explore the degree to which the stored information degrades depending upon the variation in values of various parameters involved, we suggest a set of parameters for which the original information can be retrieved without degradation. We identify a very interesting situation where the role played by the nonlinearity is insignificant, and the system behaves as if the information is stored in a linear medium. For this case, the information retrieval is independent of the coherence revival time and can be retrieved at any instant during the time evolution.

Wolfgang Tittel, Mikael Afzelius, Nicolas Gisin +2 more