Lossy Beam Splitter Research Articles

Loss-Assisted Anomalous Hong-Ou-Mandel Interference Based on Nonunitary Multilayer Graphene.

Hong-Ou-Mandel interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables numerous applications in quantum information science. While the photon-photon interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, we present that a nonunitary material provides an alternative degree of freedom to control the two-photon quantum interference, even revealing anomalous quantum interference paths that do not exist in a unitary configuration. An elaborate lossy multilayer graphene that can work as a nonunitary beam splitter is used to explore its tunability over the effective photon-photon interaction in spatial modes, and to verify the particle exchange statistics by its experimental implementation in quantum state filter. This scheme is further extended to observe four-dimensional quantum interference patterns on the lossless and lossy beam splitters, and thus show its applicability even in higher-dimensional Hilbert space.

Anti-Hong–Ou–Mandel interference by coherent perfect absorption of entangled photons

Two-photon interference, known as the Hong–Ou–Mandel effect, has colossal implications for quantum technology. It was observed in 1987 with two photodetectors monitoring outputs of the beamsplitter illuminated by photon pairs: the coincidence rate of the detectors drops to zero when detected photons overlap in time. More broadly, bosons (e.g. photons) coalesce while fermions (e.g. electrons) anti-coalesce when interfering on a lossless beamsplitter. Quantum interference of bosons and fermions can be tested in a single—photonics platform, where bosonic and fermionic states are artificially created as pairs of entangled photons with symmetric and anti-symmetric spatial wavefunctions. We observed that interference on a lossy beamsplitter of a subwavelength thickness, or a coherent perfect absorber, reverses quantum interference in such a way that bosonic states anti-coalesce while fermionic states exhibit coalescent-like behavior. The ability to generate states of light with different statistics and manipulate their interference offers important opportunities for quantum information and metrology.

Effect of loss on linear optical quantum logic gates

Linear optical quantum gates have been proposed as a possible implementation for quantum computers. Most experimental linear optical quantum gates are constructed with free-space optical components with negligible loss. In this work, we analyze symmetric and asymmetric partially polarizing lossy beam splitters. Using the generalized beam splitter equations, we study the effects of loss on two linear optical quantum gates: the first is a commonly used CNOT gate, and the second is a W state expansion gate. Envisioning inherent loss in plasmonics and metamaterials as a new degree of freedom and those materials systems as a route for miniaturization, we reconsider the requirements of the lossy CNOT gate and show it is possible to simplify the three-beam-splitter design to a single beam splitter without sacrificing success probability.

Classical simulation of linear optics subject to nonuniform losses

We present a comprehensive study of the impact of non-uniform, i.e. path-dependent, photonic losses on the computational complexity of linear-optical processes. Our main result states that, if each beam splitter in a network induces some loss probability, non-uniform network designs cannot circumvent the efficient classical simulations based on losses.To achieve our result we obtain new intermediate results that can be of independent interest. First we show that, for any network of lossy beam-splitters, it is possible to extract a layer of non-uniform losses that depends on the network geometry. We prove that, for every input mode of the network it is possible to commutesilayers of losses to the input, wheresiis the length of the shortest path connecting theith input to any output. We then extend a recent classical simulation algorithm due to P. Clifford and R. Clifford to allow for arbitraryn-photon input Fock states (i.e. to include collision states). Consequently, we identify two types of input states where boson sampling becomes classically simulable: (A) whenninput photons occupy a constant number of input modes; (B) when all butO(log⁡n)photons are concentrated on a single input mode, while an additionalO(log⁡n)modes contain one photon each.

Double-slit interferometry as a lossy beam splitter

We cast diffraction-based interferometry in the framework of post-selected unitary description towards enabling it as a platform for quantum information processing (QIP). We express slit-diffraction as an infinite-dimensional transformation and truncate it to a finite-dimensional transfer matrix by post-selecting modes. Using such a framework with classical fields we show that a customized double-slit setup is effectively a lossy beam splitter in a post-selected sense. Diffraction optics provides a robust alternative to conventional multi-beam interferometry with scope for miniaturization, and also has applications in matter wave interferometry. In this work, the classical treatment of slit-diffraction sets the stage for quantization of fields and implementing higher-dimensional QIP like that done with other platforms such as orbital angular momentum.

Nonlocal Coherent Perfect Absorption.

Coherent absorption that occurs at two spatially separated, macroscopic lossy beam splitters is described. A superposition mode of any phase can be chosen as the absorbed or transparent mode. For a nonclassical two-photon NOON-state input, a superposition of two photons entering via one of two separate input modes, a single photon can survive the pair of beam splitters with certainty, implying nonlocal absorption of a single photon, which can be detected via the interference in the two-photon survival probability.

Designing optical circuits using plasmonic beam splitters.

Plasmonic optical circuits hold great promise in reducing device footprints by orders of magnitude and enabling high device complexity. The decomposition of an arbitrary linear transformation using unitary beam splitters is well-known. However, because of the inherent lossy nature of plasmonic devices, this decomposition is not useful for the practical design of devices. In this Letter, we provide a method to design an arbitrary unitary transformation using plasmonic beam splitters, which takes into account the inherent lossy nature of plasmonic modes in the decomposition process itself, while preserving the fidelity of the transformation. We do this by selecting the loss in each arm of the beam splitters and the interconnects. We also show how this method can be extended for the case of any linear transformation by extending the singular value decomposition. This method is applicable to plasmonic and waveguide-based lossy beam splitters.

Anti-coalescence of bosons on a lossy beam splitter.

Two-boson interference, a fundamentally quantum effect, has been extensively studied with photons through the Hong-Ou-Mandel effect and observed with guided plasmons. Using two freely propagating surface plasmon polaritons (SPPs) interfering on a lossy beam splitter, we show that the presence of loss enables us to modify the reflection and transmission factors of the beam splitter, thus revealing quantum interference paths that do not exist in a lossless configuration. We investigate the two-plasmon interference on beam splitters with different sets of reflection and transmission factors. Through coincidence-detection measurements, we observe either coalescence or anti-coalescence of SPPs. The results show that losses can be viewed as a degree of freedom to control quantum processes.

Quantum interference in an asymmetric Mach-Zehnder interferometer

A re-visitation of the well known free space Mach-Zehnder interferometer is reported here. The coexistence between one-photon and two-photons interference from collinear color entangled photon pairs is investigated. Thisarises from an arbitrarily small unbalance in the arm transmittance. The tuning of such asymmetry is reflected in dramatic changes in the coincidence detection, revealing beatings between one particle and two particle interference patterns. In particular, the role of the losses and of the intrinsic phase imperfectness of the lossy beamsplitter are explored in a single-port excited Mach-Zehnder interferometer. This configuration is especially useful for quantum optics on a chip, where the guiding geometry forces photons to travel in the same spatial mode.

Increasing relative nonclassicality quantified by standard entanglement potentials by dissipation and unbalanced beam splitting

If a single-mode nonclassical light is combined with the vacuum on a beam splitter, then the output state is entangled. As proposed in [Phys. Rev. Lett. 94, 173602 (2005)], by measuring the output-state entanglement for a balanced lossless beam splitter, one can quantify the input-state nonclassicality. These measures of nonclassicality (referred to as entanglement potentials) can be based, in principle, on various entanglement measures, leading to the negativity (NP) and concurrence (CP) potentials, and the potential for the relative entropy of entanglement (REEP). We search for the maximal nonclassicality, which can be achieved by comparing two entanglement measures for arbitrary two-qubit states and those which can be generated from a photon-number qubit via a balanced lossless beam-splitter, where the qubit basis states are the vacuum and single-photon states. Surprisingly, we find that the maximal nonclassicality, measured by the REEP for a given value of the NP, can be increased (if NP<0.527) by using either a tunable beam splitter or by amplitude damping of the output state of the balanced beam splitter. We also show that the maximal nonclassicality, measured by the NP for a given value of the REEP, can be increased by dephasing. The entanglement itself is not increased by these local losses, but the possible ratios of different measures are affected. Moreover, we show that partially-mixed states can be more nonclassical than both pure states and completely-mixed states, by comparing the NP for a given value of the REEP. This implies that not all entanglement measures can be used as entanglement potentials. Alternatively, a single balanced lossless beam splitter is not always transferring the whole nonclassicality of its input state into the entanglement of its output modes. Applying a lossy beam splitter can solve this problem at least for the cases analyzed in this paper.

Interference and the lossless lossy beam splitter

Interference and the lossless lossy beam splitter

Interference and the lossless lossy beam splitter

By directing the input into a particular mode it is possible to obtain as output all of the input light for a beam splitter which is 50% absorbing. This effect is also responsible for nonlinear quantum interference when two photons are incident on the beam splitter.

Quantum optics of lossy beam splitters

The familiar input-output relations for an optical beam splitter are generalized to allow for linear absorption by the medium forming the mirror. Beam-splitter losses generally affect the noise levels detectable in experiments involving nonclassical Light. When employed to investigate two-photon interference effects, a lossy beam splitter can lead to apparent nonlinear absorption, which, in the most extreme case, leads to either both or neither of the photons being absorbed. The degree of second-order coherence of antibunched light can be maintained on transmission through the beam splitter but any amplitude squeezing in the incident light is degraded.