Quantum Correlations Of Photons Research Articles

Hiding Images in Quantum Correlations.

Photon-pair correlations in spontaneous parametric down-conversion are ubiquitous in quantum photonics. The ability to engineer their properties for optimizing a specific task is essential, but often challenging in practice. We demonstrate the shaping of spatial correlations between entangled photons in the form of arbitrary amplitude and phase objects. By doing this, we encode image information within the pair correlations, making it undetectable by conventional intensity measurements. It enables the transmission of complex, high-dimensional information using quantum correlations of photons, which can be useful for developing quantum communication and imaging protocols.

Quantum feedback induced genuine magnon–photon–magnon entanglement and steering in a cavity magnonical system

We present an alternative scheme to generate genuine tripartite entanglement and steering among one photon and two magnons in a cavity magnonical system, where two yttrium iron garnet spheres are respectively placed inside two microwave cavities driven by a two-mode squeezed field and subjected to homodyne-measurement feedback. It is found that quantum feedback on two cavities plays a crucial role in enhancing quantum correlations of photons and magnons. In the absence of measurement feedback, only bipartite entanglement between two magnons is existent. In contrast, when the continuous measurement feedback is present, two magnons are strongly entangled and magnon–photon entanglement also appears. More importantly, the stable genuine magnon–photon–magnon tripartite entanglement and steering could be obtained based on the homodyne-measurement feedback on two microwave cavities, which are robust against the thermal fluctuations. The work we present provides a feasible way to manipulate the multipartite quantum correlations including entanglement and steering in hybrid quantum systems.

Optical storage for 0.53 s in a solid-state atomic frequency comb memory using dynamical decoupling

Quantum memories with long storage times are key elements in long-distance quantum networks. The atomic frequency comb (AFC) memory in particular has shown great promise to fulfill this role, having demonstrated multimode capacity and spin–photon quantum correlations. However, the memory storage times have so-far been limited to about 1 ms, realized in a Eu3+ doped Y2SiO5 crystal at zero applied magnetic field. Motivated by studies showing increased spin coherence times under applied magnetic field, we developed an AFC spin-wave memory utilizing a weak 15 mT magnetic field in a specific direction that allows efficient optical and spin manipulation for AFC memory operations. With this field configuration the AFC spin-wave storage time increased to 40 ms using a simple spin-echo sequence. Furthermore, by applying dynamical decoupling techniques the spin-wave coherence time reaches 530 ms, a 300-fold increase with respect to previous AFC spin-wave storage experiments. This result paves the way towards long duration storage of quantum information in solid-state ensemble memories.

Topological protection of two-photon quantum correlation on a photonic chip

Low-decoherence regime plays a key role in constructing multi-particle quantum systems and has therefore been constantly pursued in order to build quantum simulators and quantum computers in a scalable fashion. Quantum error correction and quantum topological computing have been proved being able to protect quantumness but haven't been experimentally realized yet. Recently, topological boundary states are found inherently stable and are capable of protecting physical fields from dissipation and disorder, which inspires the application of such a topological protection on quantum correlation. Here, we present an experimental demonstration of topological protection of two-photon quantum states on a photonic chip. By analyzing the quantum correlation of photons out from the topologically nontrivial boundary state, we obtain a high cross-correlation and a strong violation of Cauchy-Schwarz inequality up to 30 standard deviations. Our results, together with our integrated implementation, provide an alternative way of protecting quantumness, and may inspire many more explorations in 'quantum topological photonics', a crossover between topological photonics and quantum information.

Transmission of entangled photons studied by quantum tomography: do we need plasmonic resonances?

We performed quantum tomography to reveal the robustness of quantum correlations of photons entangled in polarisation after their interaction with plasmonic and nonplasmonic environments at normal incidence. The experimental findings clearly show that the visibility of quantum correlations survives the interaction, and that the presence of plasmonic resonances has not any significant influence on the survival of polarisation correlations for transmitted photon pairs. The results indicate that quantum states can be encoded into the multiple motions of a many-body electronic system without demolishing their quantum nature. The plasmonic structures and their resonances only enhance the overall transmission. Thus, they could benefit the pair detection rate, that is the number of coincidences per unit of time, but they do not affect the visibility of quantum correlations. We also performed quantum tomography of the entangled pairs after interaction with the continuous planar gold film as a function of the incidence angle. The latter illustrates the loss of polarization correlations that arises from the partially polarizing properties of the isotropic sample out of normal incidence. Our work shows that plasmonic structures are not needed to exploit quantum entanglement if the rate of coincidence counting is sufficient.

Quantum Correlations of Photons and Qudit States

We present briefly the historical aspects of studying the properties of light including both the classical theory of light based on the electromagnetic wave picture and the quantum corpuscular interpretation of light based on the notion of photons. We consider vibrations of electric and magnetic fields in light waves and quantum correlations described by the Heisenberg and Schrodinger–Robertson uncertainty relations valid for any vibrations in connection with specific statistical properties of coherent light and squeezed light. We review the qubit and qudit states and the new uncertainty relation for entropy and energy for qudit systems. We discuss the dynamical (nonstationary) Casimir effect providing a vacuum generator of squeezed photons based on the technique of superconducting circuits realized by Josephson junctions. We demonstrate new entropic inequalities for two qubits (polarization states of two photons) and hidden correlations of noncomposite quantum systems (quantum roulette).

An Analogy Between the Properties of Light and Properties of Vortex-Wave Process in the Medium Similar to Superfluid <SUP>3</SUP>Не-В

Characteristics of three types of photon used in the descriptions of optical experiments demonstrating the properties of light are discussed: C-photon – a quasi-monochromatic electromagnetic radiation localized in space, M-photon – a hypothetical elementary particle of the light field, and Q-photon – an objective entity corresponding to the Fock state of the light field. Some properties of superfluid 3Не-В are analyzed and equations are derived describing a vortex-wave process in the medium similar to superfluid 3Не-В. The comparison of the properties of light and those of vortex-wave process in the medium similar to superfluid 3Не-В shows that there is an analogy between the properties of light and the properties of the process. The analogy found allows one to offer a physical model describing such properties of light as the constancy of its speed in inertial frames of reference, and quantum correlations of photons.

The Non-Electromagnetic Action of Photons on Biological Systems. Spin Supercurrent

The paper aims at showing that there is a physical process that might account for the non-electromagnetic action of photons on biological systems. An analogy is shown between the effects of low-intensity electromagnetic radiation and the effects of biologically active substances in ultra-low doses on biological systems and also the features of quantum correlation of photons. The analogy may be due to the same physical mechanism underlying the phenomena. It is of importance that quantum correlations of photons are effected by non-electromagnetic forces. A comparison is drawn between the features of quantum correlations in such quantum macrosystem as superfluid 3He-B and the experimentally established properties of quantum correlations of photons. It is shown that quantum correlations (and, consequently, the effects of low-intensity electromagnetic radiation on biological systems) may be due to spin supercurrents, whose properties are like those of spin supercurrents emerging between spin structures in superfluid 3He-B, the spin supercurrents being of non-electromagnetic nature. It is shown that the non-electromagnetic action of photons on a biological system may be performed by spin supercurrents emerging between the spin structures produced by the photons and biological system in the physical vacuum. The spin supercurrent speed may exceed that of light, because the spin supercurrent is not accompanied by the birth of a mass, as it is in the motion of a body (the relativistic increase in mass) or in the motion of photon (the kinetic mass of photon), and therefore has no inertial properties

Quantum-correlated two-photon transitions to excitons in semiconductor quantum wells

The dependence of the excitonic two-photon absorption on the quantum correlations (entanglement) of exciting biphotons by a semiconductor quantum well is studied. We show that entangled photon absorption can display very unusual features depending on space-time-polarization biphoton parameters and absorber density of states for both bound exciton states as well as for unbound electron-hole pairs. We report on the connection between biphoton entanglement, as quantified by the Schmidt number, and absorption by a semiconductor quantum well. Comparison between frequency-anti-correlated, unentangled and frequency-correlated biphoton absorption is addressed. We found that exciton oscillator strengths are highly increased when photons arrive almost simultaneously in an entangled state. Two-photon-absorption becomes a highly sensitive probe of photon quantum correlations when narrow semiconductor quantum wells are used as two-photon absorbers.

Observation of Spatial Quantum Correlations Induced by Multiple Scattering of Nonclassical Light

We present the experimental realization of spatial quantum correlations of photons that are induced by multiple scattering of squeezed light. The quantum correlation relates photons propagating along two different light paths through the random medium and is infinite in range. Both positive and negative spatial quantum correlations are observed when varying the quantum state incident to the multiple scattering medium, and the strength of the correlations is controlled by the number of photons. The experimental results are in excellent agreement with recent theoretical proposals by implementing the full quantum model of multiple scattering.

Pulse-mode study of the quantum correlation of photons in anN-photon Dicke model

Abstract We find the N-photon state emitted by an N-step Dicke model and provide a method to construct the field coherence functions based on it. Our effort is concentrated on the second order coherence, or the one-photon density matrix. When expressed in its canonical representation, this matrix gives the photon number occupying each ‘pulse eigenmode’. This number serves as an indicator of the correlation between photons. By studying the evolution of the one-photon density matrix we can trace the creation of such correlation during the emission. From the asymptotic solution we are able to find approximate scaling law relations between the photon degeneracy in the eigenmodes and the total number of photons involved.

Pulse-mode study of the quantum correlation of photons in an N-photon Dicke model

Abstract We find the N-photon state emitted by an N-step Dicke model and provide a method to construct the field coherence functions based on it. Our effort is concentrated on the second order coherence, or the one-photon density matrix. When expressed in its canonical representation, this matrix gives the photon number occupying each ‘pulse eigenmode’. This number serves as an indicator of the correlation between photons. By studying the evolution of the one-photon density matrix we can trace the creation of such correlation during the emission. From the asymptotic solution we are able to find approximate scaling law relations between the photon degeneracy in the eigenmodes and the total number of photons involved.