Quantum Photon States Research Articles

First-order optical coherence of photonic-dimer coherent states.

Photon-photon correlations assume a pivotal significance in optical coherence. Recently, a new, to the best of our knowledge, type of quantum photonic states, the coherent state of photonic dimers, has been introduced, wherein the fundamental building blocks are two-photon bound states, instead of individual photons as in conventional lasers. In this Letter, we investigate the first-order coherence properties of the photonic-dimer coherent states, as well as the interference patterns in a double-slit interferometer setup, and compare with the coherence properties of other optical light sources, e.g., the conventional laser and the thermal light.

Universal Control of Symmetric States Using Spin Squeezing.

The manipulation of quantum many-body systems is a crucial goal in quantum science. Entangled quantum states that are symmetric under qubits permutation are of growing interest. Yet, the creation and control of symmetric states has remained a challenge. Here, we introduce a method to universally control symmetric states, proposing a scheme that relies solely on coherent rotations and spin squeezing. We present protocols for the creation of different symmetric states including Schrödinger's cat and Gottesman-Kitaev-Preskill states. The obtained symmetric states can be transferred to traveling photonic states via spontaneous emission, providing a powerful approach for engineering desired quantum photonic states.

Photonic Fock state generation using superradiance.

Photonic Fock states are the most basic quantum states of a radiation field, but arbitrary number states are still difficult to produce. Here we propose to use superradiant atoms in a chiral waveguide to generate multi-photon Fock states deterministically. We calculate the explicit forms of the output quantum photonic states and their correlation functions. We further establish the conditions for the output optical fields to approach the Fock states asymptotically.

Weakly invasive metrology: quantum advantage and physical implementations

We consider the estimation of a Hamiltonian parameter of a set of highly photosensitive samples, which are damaged after a few photons Nabs are absorbed, for a total time T. The samples are modelled as a two mode photonic system, where photons simultaneously acquire information on the unknown parameter and are absorbed at a fixed rate. We show that arbitrarily intense coherent states can obtain information at a rate that scales at most linearly with Nabs and T, whereas quantum states with finite intensity can overcome this bound. We characterise the quantum advantage as a function of Nabs and T, as well as its robustness to imperfections (non-ideal detectors, finite preparation and measurement rates for quantum photonic states). We discuss an implementation in cavity QED, where Fock states are both prepared and measured by coupling atomic ensembles to the cavities. We show that superradiance, arising due to a collective coupling between the cavities and the atoms, can be exploited for improving the speed and efficiency of the measurement.

Shaping quantum photonic states using free electrons.

It is a long-standing goal to create light with unique quantum properties such as squeezing and entanglement. We propose the generation of quantum light using free-electron interactions, going beyond their already ubiquitous use in generating classical light. This concept is motivated by developments in electron microscopy, which recently demonstrated quantum free-electron interactions with light in photonic cavities. Such electron microscopes provide platforms for shaping quantum states of light through a judicious choice of the input light and electron states. Specifically, we show how electron energy combs implement photon displacement operations, creating displaced-Fock and displaced-squeezed states. We develop the theory for consecutive electron-cavity interactions with a common cavity and show how to generate any target Fock state. Looking forward, exploiting the degrees of freedom of electrons, light, and their interaction may achieve complete control over the quantum state of the generated light, leading to novel light statistics and correlations.

Topological Nanophotonics: Toward Robust Quantum Circuits

In the last five years, the combination of advances in nanofabrication and a series of ingenious design ideas has enabled the implementation of topological concepts into nanophotonic platforms. In parallel, an unprecedented amount of research effort is being devoted to quantum technologies, with quantum information processing promising exponentially better performance than its classic counterpart for certain tasks. Nanophotonics is bound to play a key role in quantum information technologies given its compactness, low-power requirements, room-temperature operation, and the inherent high speed and low noise of photons. However, the scalability of quantum information systems in integrated photonic platforms is limited by scattering loss and other errors from random fabrication imperfections. The remarkable robustness to disorder and imperfections manifested by photonic states in topological systems emerges as a fascinating research avenue to tackle this issue. Furthermore, the ease of engineering and fabricating nanophotonic platforms with distinctive geometries and symmetries that can effectively generate and transport complex quantum states makes nanophotonics an ideal platform in which to realize topological protection of quantum photonic states. This article highlights the pioneering experimental efforts to understand the potential of topological protection on quantum photonic states and to outline a path toward robust quantum circuits.

Multiphoton Interference in the Spectral Domain by Direct Heralding of Frequency Superposition States.

Multiphoton interference is central to photonic quantum information processing and quantum simulation, usually requiring multiple sources of nonclassical light followed by a unitary transformation on their modes. We observe interference in the four-photon events generated by a single silicon waveguide, where the different modes are six frequency channels. Rather than requiring a unitary transformation, the frequency correlations of the source are configured such that photons are generated in superposition states across multiple channels, and interference effects can be seen without further manipulation. The frequency correlations of the source also mean that it is effectively acting as multiple pair photon sources, generating photons in different spectral modes, which interfere with each other in a nontrivial manner. This suggests joint spectral engineering is a tool for controlling complex quantum photonic states without the difficulty of implementing spatially separate sources or a large unitary interferometer, which could have practical benefits in various applications of multiphoton interference.

Photon-pair generation in a quadratically nonlinear parity-time symmetric coupler

Integrated nonlinear waveguide structures enable generation of quantum entangled photons. We describe theoretically the effects of spatially inhomogeneous loss on the creation of photon pairs through spontaneous parametric down-conversion in quadratically nonlinear directional couplers, where photons experience effective parity-time (PT) symmetric potential due to the presence of optical loss in one of the waveguides. We show that for losses below the PT-breaking threshold, the quantum photon states can be flexibly tuned similarly to conservative couplers, whereas for stronger losses, the correlations between two waveguide modes are suppressed. We also formulate a quantum-classical correspondence with sum-frequency generation for fast evaluation of device performance. These results can be applied for the design of quantum plasmonic circuits.

Tunable generation of entangled photons in a nonlinear directional coupler

AbstractThe on‐chip integration of quantum light sources has enabled the realization of complex quantum photonic circuits. However, for the practical implementation of such circuits in quantum information applications, it is crucial to develop sources delivering entangled quantum photon states with on‐demand tunability. Here we propose and experimentally demonstrate the concept of a widely tunable quantum light source based on spontaneous parametric down‐conversion in a simple nonlinear directional coupler. We show that spatial photon‐pair correlations and entanglement can be reconfigured on‐demand by tuning the phase difference between the pump beams and the phase mismatch inside the structure. We experimentally demonstrate the generation of split states, robust N00N states, various intermediate regimes and biphoton steering on a single chip. Furthermore we theoretically investigate other regimes allowing all‐optically tunable generation of all Bell states and flexible control of path‐energy entanglement. Such wide‐range capabilities of a structure comprised of just two coupled nonlinear waveguides are attributed to the intricate interplay between linear coupling and nonlinear phase matching. This scheme provides an important advance towards the realization of reconfigurable quantum circuitry. image

New perspectives in the generation of entangled qudit states

We present a new experimental technique to generate multilevel quantum photon states based on the linear momentum degree of freedom of the photons emitted by the spontaneous parametric down conversion process.

Generation of quantum photon states in an active microcavity trap

Generation of quantum photon states in an active microcavity trap

Generation of quantum photon states in an active microcavity trap

The active microcavity is adopted as an efficient source of non-classical light. By this device, excited by a mode-locked laser at a rate of 100 MHz, single photons are generated over a single field mode with a non-classical sub-Poissonian distribution. The process of adiabatic recycling within a multistep Franck–Condon molecular optical-pumping mechanism, characterized in our case by a quantum efficiency close to one, implies a pump self-regularization process leading to a striking n-squeezing effect. Moreover, the microactivity has been adopted as active beam splitter in a novel Hanbury-Brown–Twiss configuration for the radiation taking place over the two output mirrors. By a replication of the basic single-atom excitation process a beam of quantum photon |n⟩ states (Fock states) can be created. The new process may represent a significant advance in the modern fields of basic quantum-mechanical investigation, quantum communication and quantum cryptography.

Single-mode generation of quantum photon states by excited single molecules in a microcavity trap.

The active microcavity is adopted as an efficient source of non-classical light. By this device, excited by a mode-locked laser at a rate of 100 MHz, single-photons are generated over a single field mode with a nonclassical sub-poissonian distribution. The process of adiabatic recycling within a multi-step Franck-Condon molecular optical-pumping mechanism, characterized in our case by a quantum efficiency very close to one, implies a pump self-regularization process leading to a striking n-squeezing effect. By a replication of the basic single-atom excitation process a beam of quantum photon |n> - states (Fock states) can be created. The new process represents a significant advance in the modern fields of basic quantum-mechanical investigation, quantum communication and quantum cryptography.