Nonlinear optical effects such as frequency conversion form the basis for many practical light sources. In a variety of settings, the performance of such sources is limited by quantum noise. In many nonlinear systems, this quantum noise gets strongly amplified, as a result of the large sensitivity of the nonlinear dynamics to changes in the initial conditions - a feature common to many nonlinear systems. Here, we develop a general theory of quantum noise resulting from nonlinear dynamics initiated by many-photon Gaussian quantum states. The theory provides guidelines to find the optimal quantum state to inject to maximally suppress the noise at the output. As a concrete example of the concept and theory, we consider the nonlinear optical phenomenon of supercontinuum generation by a femtosecond pulse, a famously noise-generating process, which is important in a range of applications in materials characterization and life science. By seeding supercontinuum generation with pulsed squeezed vacuum, one can achieve order-of-magnitude magnitude reduction of intensity and phase noise simultaneously, over a broad band of wavelengths, passively, and with no change in spectrum. The large magnitude and bandwidth of this effect is challenging to achieve by other means of stabilization, pointing to a promising approach for controlling quantum noise in a variety of nonlinear systems.
Nonlinear optical effects such as frequency conversion form the basis for many practical light sources. In a variety of settings, the performance of such sources is limited by quantum noise. In many nonlinear systems, this quantum noise gets strongly amplified, as a result of the large sensitivity of the nonlinear dynamics to changes in the initial conditions - a feature common to many nonlinear systems. Here, we develop a general theory of quantum noise resulting from nonlinear dynamics initiated by many-photon Gaussian quantum states. The theory provides guidelines to find the optimal quantum state to inject to maximally suppress the noise at the output. As a concrete example of the concept and theory, we consider the nonlinear optical phenomenon of supercontinuum generation by a femtosecond pulse, a famously noise-generating process, which is important in a range of applications in materials characterization and life science. By seeding supercontinuum generation with pulsed squeezed vacuum, one can achieve order-of-magnitude magnitude reduction of intensity and phase noise simultaneously, over a broad band of wavelengths, passively, and with no change in spectrum. The large magnitude and bandwidth of this effect is challenging to achieve by other means of stabilization, pointing to a promising approach for controlling quantum noise in a variety of nonlinear systems.
In reality, a wide variety of laser sources have fluctuations in excess (and often far in excess) of the coherent state, even when technical noise sources are suppressed. I present recent advances that challenge this paradigm, and show how multimode nonlinearities can be steered towards reducing the noise of intense beams of light down to quantum limits associated with coherent states and squeezed states of light. I will show how multimode correlations and wavefront shaping can suppress excess noise by orders of magnitude: reaching, and even surpassing, the shot-noise limit. We demonstrate these effects for femtosecond pulses propagating in both single-mode fibers and in multi-mode fibers. Our ability to control noise is aided by a general theory framework that we have developed, called quantum sensitivity analysis, which lets us predict how quantum noise is transformed by nonlinear and multimode systems.
Quantum states of light, particularly at optical frequencies, are considered necessary to realize a host of important quantum technologies and applications, spanning Heisenberg-limited metrology, continuous-variable quantum computing, and quantum communications. Nevertheless, a wide variety of important quantum light states are currently challenging to deterministically generate at optical frequencies. In part, this is due to a relatively small number of schemes that prepare target quantum states given nonlinear interactions. Here, we present an especially simple concept for deterministically generating and stabilizing important quantum states of light, using only third-order optical nonlinearities and engineered dissipation. We show how, by considering either a nonlinear cavity with frequency-dependent outcoupling or a chain of nonlinear waveguides, one can induce high loss for all but some desired light intensities. Specifically, we find that the stabilized intensities can correspond to an evenly spaced pattern of stablilized photon numbers. This is shown to produce important quantum states with coherent superpositions between various photon numbers. As examples of this phenomenon, we show cavities which can stabilize squeezed states, as well as produce "photon-number-comb" states. Moreover, in these types of filter cavities, Glauber coherent states will deterministically evolve into Schrodinger cat states of a desired order. We discuss potential realizations in quantum nonlinear optics. More broadly, we expect that combining the techniques introduced here with additional "phase-sensitive" nonlinearities (such as second-order nonlinearity) should enable passive stabilization and generation of a wider variety of states than shown here.
Quantum states of light, particularly at optical frequencies, are considered necessary to realize a host of important quantum technologies and applications, spanning Heisenberg-limited metrology, continuous-variable quantum computing, and quantum communications. Nevertheless, a wide variety of important quantum light states are currently challenging to deterministically generate at optical frequencies. In part, this is due to a relatively small number of schemes that prepare target quantum states given nonlinear interactions. Here, we present an especially simple concept for deterministically generating and stabilizing important quantum states of light, using only simple third-order optical nonlinearities and engineered dissipation. We show how by considering either a nonlinear cavity with frequency-dependent outcoupling, or a chain of nonlinear waveguides, one can "filter" out all but a periodic ladder of photon number components of a density matrix. As examples of this phenomenon, we show cavities which can stabilize squeezed states, as well as produce "photon-number-comb" states. Moreover, in these types of filter cavities, Glauber coherent states will deterministically evolve into Schrodinger cat states of a desired order. We discuss potential realizations in quantum nonlinear optics. More broadly, we expect that combining the techniques introduced here with additional "phase-sensitive" nonlinearities (such as second-order nonlinearity) should enable passive stabilization and generation of a wider variety of states than shown here.
Nonlinear dynamics provide an indispensable resource for creating quantum states of light, as well as other bosonic systems. Seminal work using second- and third-order nonlinear optical crystals, cavity quantum electrodynamics, and superconducting circuits, have enabled generating squeezed states, as well as various non-Gaussian quantum states (e.g., single photons, cat states) at both infrared and microwave frequencies. Nevertheless, it remains challenging to generate quantum states of light in broad portions of the electromagnetic spectrum: for example, at terahertz frequencies and at ultraviolet and X-ray frequencies. In this Perspective, I discuss a variety of emerging material platforms, as well as emerging theoretical and experimental tools, which enable overcoming these challenges. The main argument of this Perspective is that advances in driving nonlinear dynamics of material excitations, will enable generating quantum states of these material excitations as well as quantum states of light at new frequency ranges. I will further argue that in order to realize much of the promise of this nascent field, there is a need for innovation in the laser systems used to drive these nonlinear dynamics: specifically, innovations in realizing high-power laser sources that have very low noise, having quantum statistics similar to coherent states of light which describe lower intensity laser systems. I will highlight some experimental and theoretical work, in understanding quantum noise dynamics in complex laser systems, that can address these challenges.
Abstract The generation and application of squeezed light have long been central goals of quantum optics. Intensity noise squeezing of bright (coherent) states (“bright squeezing”), in contrast to squeezed vacuum, is relatively underdeveloped. The current state of the art has generally been restricted to narrow operating wavelength ranges and does not natively support strong intracavity and broadband output squeezing. Here, we show how lasers with sharp intensity‐dependent dissipation can support strong intensity noise squeezing from infrared (IR) to terahertz (THz) wavelengths, the latter of which has eluded quantum light generation. Our protocol realizes strongly ( dB) intensity noise‐squeezed intracavity quantum states as well as output squeezing surpassing gigahertz bandwidths. Furthermore, we show how the same systems also support self‐pulsing and bistability, enabling control of light in both the mean field and noise domains. Our protocol could enable advances in low‐noise communication, cavity QED, and quantum sensing across the electromagnetic spectrum.