Experimental generation of quantum entanglement and testing fundamentals of quantum physics

Raffaele Silvestri, Haocun Yu, Teodor Strömberg +3 more

Precision interferometry with quantum states has emerged as an essential tool for experimentally answering fundamental questions in physics. Optical quantum interferometers are of particular interest because of mature methods for generating and manipulating quantum states of light. Their increased sensitivity promises to enable tests of quantum phenomena, such as entanglement, in regimes where tiny gravitational effects come into play. However, this requires long and decoherence-free processing of quantum entanglement, which, for large interferometric areas, remains unexplored territory. Here, we present a table-top experiment using maximally path-entangled quantum states of light in a large-scale interferometer sensitive enough to measure the rotation rate of Earth. The achieved sensitivity of 5 μrad s −1 constitutes the highest rotation resolution ever reached with optical quantum interferometers. Further improvements to our methodology will enable measurements of general-relativistic effects on entangled photons, allowing the exploration of the interplay between quantum mechanics and general relativity, along with tests for fundamental physics.

Daniel R. Bes

Haruka Terashima, Satoshi KOBAYASHI, Takaho Tsubakiyama +1 more

Quantum interference, like Hong-Ou-Mandel interference, has played an important role to test fundamental concepts in quantum physics. We experimentally show that the multiple quantum interference effects enable the generation of high-performance polarization entangled photons. These photons have a high-emission rate, are degenerate, have a broadband distribution, and are postselection free. A quantum interferometric scheme, based on a round-trip configuration of a double-pass polarization Sagnac interferometer, makes it possible to use the large generation efficiency of polarization entangled photons in the process of parametric down-conversion and to separate degenerate photon pairs into different optical modes with no requirement of postselection. We demonstrate experimentally that multiple quantum interference is not only an interesting fundamental quantum optical phenomenon but can be used for novel photonic quantum information technologies.

F.J. Duarte

Časlav Brukner

Byoung Seung HAM

Quantum technologies based on the particle nature of a photon has been progressed over the last several decades, where the fundamental quantum feature of entanglement has been tested by Hong-Ou-Mandel (HOM) type anticorrelation as well as Bell-type nonlocal correlation. Mutually exclusive quantum natures of the wave-particle duality of a single photon have been intensively investigated to understand the fundamental physics of mysterious quantum nature. Here, we revisit the HOM-type quantum correlation to answer the question whether the HOM-type anticorrelation can be a test tool for quantum entanglement. For this, a pair of spontaneous parametric down converted photons is tested for the anticorrelation of HOM effects, where the SPDC-generated photon pair is not in an entangled state.