Highly coherent frequency-entangled photons based on parametric instability in active fiber ring cavity

Highly coherent frequency-entangled photons at telecom band are critical in quantum information protocols and quantum tele-communication. Photon pairs generated by spontaneous parametric down-conversion in nonlinear crystals or modulation instability in optical fibers exhibit random fluctuations. Here, we demonstrate highly stable frequency-entangled photons based on parametric instability in an active fiber ring cavity, where periodic modulation of dispersion excites parametric resonance, and the characteristic wave number is selected by the periodic modulation of resonator. Background-free autocorrelation of single-shot spectra reveals that spectra of parametric instability sidebands possess high coherence. The quantum properties are tested by the Hanbury Brown-Twiss measurement and Hong-Ou-Mandel interference. We conform the frequency-entanglement of two parametric instability sidebands by a spatial quantum beating with a fringe visibility of 97.9%. Our results prove that the parametric instability in active fiber cavity is effective to generate highly coherent frequency-entangled photon pairs, which would facilitate subsequent quantum applications.

Quantum imaging of a polarisation sensitive phase pattern with hyper-entangled photons

A transparent polarisation sensitive phase pattern makes a polarisation dependent transformation of quantum state of photons without absorbing them. Such an invisible pattern can be imaged with quantum entangled photons by making joint quantum measurements on photons. This paper shows a long path experiment to quantum image a transparent polarisation sensitive phase pattern with hyper-entangled photon pairs involving momentum and polarisation degrees of freedom. In the imaging configuration, a single photon interacts with the pattern while the other photon, which has never interacted with the pattern, is measured jointly in a chosen polarisation basis and in a quantum superposition basis of its position which is equivalent to measure its momentum. Individual photons of each hyper-entangled pair cannot provide a complete image information. The image is constructed by measuring the polarisation state and position of the interacting photon corresponding to a measurement outcome of the non-interacting photon. This paper presents a detailed concept, theory and free space long path experiments on quantum imaging of polarisation sensitive phase patterns.

Psychophysical interactions with entangled photons

Objective: Four laboratory studies and an online experiment explored psychophysical (mind-matter) interactions with quantum entangled photons. Method: Entanglement correlation strength measured in real-time was presented via a graph or dynamic images displayed on a computer monitor or web browser. Participants were tasked with mentally influencing that metric. Results: A statistically significant increase in entanglement strength was obtained in experimental conditions in the four lab studies (p < 0.02), with particularly strong results observed in three studies conducted at the Institute of Noetic Sciences (p < 0.0002). Modest results (p < 0.05) were observed in a high-quality subset of entanglement samples in an online experiment. Control experiments using the same equipment and protocols, but without observers present, showed results consistent with chance expectation in both the lab and online studies. Conclusion: These outcomes suggest that the fidelity of entangled states and the nonlocal resource they entail may be mutable in systems that include conscious awareness. This is potentially of interest for quantum information technologies such as quantum computation, encryption, key distribution, and teleportation. The results are also relevant for interpretations of quantum theory, especially if future studies show that entanglement strength can be mentally modulated above the Tsirelson Bound – the upper limit predicted by quantum theory. Such an outcome would suggest that quantum theory in its present form does not hold when physical systems interact with certain mental states. The results of these exploratory experiments justify continued investigation of entangled photons as targets of mind-matter interaction.

Optimal strategy to certify quantum nonlocality

Certification of quantum nonlocality plays a central role in practical applications like device-independent quantum cryptography and random number generation protocols. These applications entail the challenging problem of certifying quantum nonlocality, something that is hard to achieve when the target quantum state is only weakly entangled, or when the source of errors is high, e.g. when photons propagate through the atmosphere or a long optical fiber. Here we introduce a technique to find a Bell inequality with the largest possible gap between the quantum prediction and the classical local hidden variable limit for a given set of measurement frequencies. Our method represents an efficient strategy to certify quantum nonlocal correlations from experimental data without requiring extra measurements, in the sense that there is no Bell inequality with a larger gap than the one provided. Furthermore, we also reduce the photodetector efficiency required to close the detection loophole. We illustrate our technique by improving the detection of quantum nonlocality from experimental data obtained with weakly entangled photons.