Unlike one-photon (first order) intensity correlation, two-photon (second order) intensity correlation is known to be impossible to achieve by any classical means. Over the last several decades, such quantum features have been intensively demonstrated for anti-correlation in the Hong-Ou-Mandel effects and nonlocal correlation in Bell inequality violation. Here, we present coherence manipulations of attenuated laser light to achieve such a quantum feature using pure coherence optics. Unlike the common understanding of the two-photon intensity correlations, the present coherence approach gives an equivalent classical version to the known quantum approach. To excite the coherence quantum features between paired coherent photons, a selective measurement process plays an essential role in creating the inseparable joint phase relation between independent local parameters. The local randomness is also satisfied in both parties using orthonormal polarization bases of a single photon.
Unlike one-photon (first order) intensity correlation, two-photon (second order) intensity correlation is known to be impossible to achieve by any classical means. Over the last several decades, such quantum features have been intensively demonstrated for anti-correlation in the Hong-Ou-Mandel effects and nonlocal correlation in Bell inequality violation. Here, we present coherence manipulations of attenuated laser light to achieve such a quantum feature using pure coherence optics. Unlike the common understanding of the two-photon intensity correlations, the present coherence approach gives an equivalent classical version to the known quantum approach. To excite the coherence quantum features between paired coherent photons, a selective measurement process plays an essential role in creating the inseparable joint phase relation between independent local parameters. The local randomness is also satisfied in both parties using orthonormal polarization bases of a single photon.
Quantum entanglement is known as a unique quantum feature that cannot be obtained by classical physics. Over the last several decades, however, such an understanding on quantum entanglement might have confined us in a limited world of weird quantum mechanics. Unlike a single photon, a definite phase relation between paired photons is the key to understanding quantum features. Recently, an intuitive approach to the otherwise mysterious quantum features has emerged and shined a light on coherence manipulations of product-basis superposition via selective measurements. Here, a coherence manipulation is presented to excite polarization-path correlation using Poisson-distributed coherent photons for a classically excited joint-phase relation of independent local parameters. For this, linear optics is used for the preparation of the polarization-basis randomness, and a gated heterodyne detection technique is adopted for the selective measurement of polarization bases. As a result, the nonlocal quantum feature is now coherently understood in a deterministic way.
Quantum entanglement generation is generally known to be impossible by any classical means. According to Poisson statistics, coherent photons are not considered quantum particles due to the bunching phenomenon. Recently, a coherence approach has been applied for quantum correlations such as the Hong-Ou-Mandel (HOM) effect, Franson-type nonlocal correlation, and delayed-choice quantum eraser to understand the mysterious quantum features. In the coherence approach, the quantum correlation has been now understood as a direct result of selective measurements between product bases of phase-coherent photons. Especially in the HOM interpretation, it has been understood that a fixed sum-phase relation between paired photons is the bedrock of quantum entanglement. Here, a coherently excited HOM model is proposed, analyzed, and discussed for the fundamental physics of two-photon correlation using linear optics-based polarization-basis control. For this, polarization-frequency correlation in a Mach-Zehnder interferometer is coherently excited using synchronized acousto-optic modulators, where polarization-basis control is conducted via a selective measurement process of the heterodyne signals. Like quantum operator-based destructive interference in the HOM theory, a perfectly coherent analysis shows the same HOM effects of the paired coherent photons on a beam splitter, whereas individual output intensities are uniform.
Franson-type nonlocal quantum correlation based on the particle nature of quantum mechanics has been intensively studied for both fundamental physics and potential applications of quantum key distribution between remotely separated parties over the last several decades. Recently, a coherence theory of deterministic quantum features has been applied for Franson-type nonlocal correlation [arXiv:2102.06463] to understand its quantumness in a purely classical manner, where the resulting features are deterministic and macroscopic. Here, nearly sub-Poisson distributed coherent photon pairs obtained from an attenuated laser are used for the experimental demonstrations of the coherence Franson-type nonlocal correlation. As an essential requirement of quantum mechanics, quantum superposition is macroscopically provided using polarization basis-randomness via a half-wave plate, satisfying fairness compared with the original scheme based on phase bases. The observed coherence quantum feature of the modified Franson correlation successfully demonstrates the proposed wave nature of quantum mechanics, where the unveiled nonlocal correlation is relied on a definite phase relation between the paired coherent photons.
Nonlocal quantum correlation has been the main issue of quantum mechanics over the last century. The Hong-Ou-Mandel (HOM) effect relates to the two-photon intensity correlation on a beam splitter, resulting in a nonclassical photon-bunching phenomenon. The HOM effect has been used to verify the quantum feature via Bell measurements for quantum technologies such as quantum repeaters and photonics quantum computing. Here, a coherence version of the HOM effect is proposed and analyzed to understand the fundamental physics of the anticorrelation and entanglement. For this, frequency-correlated coherent photon pairs are prepared in an independent set of Mach-Zhender interferometers (MZI) using a synchronized pair of modulators from an attenuated laser. For the HOM effect, the phase relation between frequency-correlated photons plays an essential role. For the product-basis randomness, the symmetrically modulated two independent MZIs are combined together incoherently. A classical intensity product between two independent photodetectors is also discussed for the same HOM effect in a selective macroscopic measurement scheme.
Abstract Photon indistinguishability is an essential concept to understanding “mysterious” quantum features from the viewpoint of the wave-particle duality in quantum mechanics. The physics of indistinguishability lies in the manipulation of quantum superposition between orthonormal bases of a single photon such as in a quantum eraser. Here, a pure coherence approach is applied for the nonlocal correlation based on the polarization-frequency correlation of Poisson-distributed coherent photon pairs to investigate the role of quantum measurements. For this, a gated heterodyne-detection technique is adopted for coincidence measurements between space-like separated delayed-choice quantum erasers, resulting in an inseparable basis product between them. Thus, the mysterious quantum correlation is coherently understood via a tensor-product modification for the second-order quantum superposition. Finally, the Bell inequality violation is numerically confirmed for the derived coherence solutions of the nonlocal correlation.
Quantum entanglement between paired photons is the foundation of optical quantum computing, quantum sensing, and quantum networks. Traditionally, quantum information science has focused on the particle nature of photons at the microscopic scale, often neglecting the phase information of single photons, even for the bipartite quantum entanglement. Recently, a coherence-based approach has been explored to understand the so-called quantum mystery of nonlocal intensity fringes emerging from local randomness. Here, a pure coherence method is presented to create macroscopic quantum features using conventional laser light via linear optics-based measurement modifications. To achieve this, a polarization-basis control of the laser light is conducted to generate indistinguishable characteristics between orthogonally polarized light pairs. Using projection measurements of the polarization-controlled light pairs, we derive coherence solutions of local randomness and nonlocal correlations between independently controlled local parameters, where a fixed relative phase relationship between paired lights is an essential condition to determine the corresponding Bell states.