Photonics: Nature in reverse

Y. V. G. S. Murti, Cherianath Vijayan

M. Dinu, I. Miotkowski, David D. Nolte

Summary form only given. Phase conjugation is a nonlinear optical process that reverses the wavefront of a beam of light and which is mathematically analogous to the time-reversal of the wave. It is therefore natural to ask whether this analogy is physically significant. Because photons are bosons, quantum properties can emerge at the macroscopic level. Such a quantum-mechanical property is the geometric (Berry's) phase acquired by cycling a photon on a closed circuit in phase space (which for polarization states is the Poincare sphere). Berry's phase can be considered to be a record of the system history and therefore can be used to gain insight into its time-invariance properties. Also, the large magneto-optical effects experienced by photorefractive diluted magnetic semiconductors suggest a natural experimental situation for probing the nature of time reversal in phase conjugation by studying the effect of applied magnetic fields on phase-conjugate light. It has been previously shown that the application of a magnetic field leads to the quenching of the time-reversed polarization state of the phase-conjugate beam in four-wave mixing experiments. We propose an experiment to further explore the influence of magnetic fields on time reversal.

Rachel Pei Chin Won

Peter Schiansky, Teodor Strömberg, David Trillo +4 more

In quantum mechanics, the unitary nature of time evolution makes it intrinsically reversible, given control over the system in question. Remarkably, there have been several recent demonstrations of protocols for reverting unknown unitaries in scenarios where even the interactions with the target system are unknown. These protocols are limited by their probabilistic nature, raising the fundamental question of whether time-reversal could be performed deterministically. Here we show that quantum physics indeed allows for this by exploiting the non-commuting nature of quantum operators, and demonstrate a recursive protocol for two-level quantum systems with an arbitrarily high probability of success. Using a photonic platform, we achieve an average rewinding fidelity of over 95%. Our protocol, requiring no knowledge of the quantum process to be rewound, is optimal in its running time, and brings quantum rewinding into a regime of practical relevance.

Erhan Sağlamyürek, Neil E. Sinclair, Jeongwan Jin +7 more

For advanced applications in quantum information and communication the reversible transfer of quantum information between light and matter is essential. A key property of such a light-matter quantum interface is the faithful mapping of entanglement. We report the reversible transfer of photon-photon entanglement into entanglement between a photon and a collective atomic excitation in a thulium-doped lithium niobate waveguide. We use an Atomic Frequency Comb (AFC) memory protocol yielding a 5 GHz acceptance bandwidth of our memory. We reconstruct the bi-photon quantum state before and after the reversible transfer and asses the entanglement-preserving nature of our memory. We demonstrate a near perfect mapping of the entangled state. Additionally, we measure a violation of the CHSH Bell inequality before and after storage, thus directly verifying the sufficiency of the entanglement for quantum communication.

Felix Cheung