Bright Squeezed Vacuum Achieves Deterministic Non-Gaussianity, Enabling Advanced Quantum Computing

Non-Gaussian states of light represent a crucial advancement for secure quantum computing and precision measurement, but generating these states typically results in weak signals. Andrei Rasputnyi, Ilya Karuseichyk, Gerd Leuchs, and colleagues at the Max Planck Institute for the Science of Light, Laboratoire d’Optique Appliquée, and Polytechnique Montréal now demonstrate a method for creating a strong, readily detectable non-Gaussian state by harnessing a phenomenon called the Kerr effect within a bright squeezed vacuum. The team directly observes a transformation of the light’s statistical properties, shifting from a Gaussian distribution to a distinctive ‘S’ shape, which confirms the influence of this nonlinear process. This achievement overcomes a significant limitation in the field, offering a pathway to applications demanding high photon numbers and bridging the gap between conventional optics and ultrafast nonlinear optics.

Non-Gaussian states of light are a critical resource for fault-tolerant quantum computing and enhanced metrology, but are typically faint and often obtained via post-selection. Researchers demonstrate the deterministic generation of a bright non-Gaussian state by introducing a Kerr nonlinearity, a process that alters the properties of light as it passes through a material. This approach circumvents the limitations of traditional methods that rely on probabilistic generation and subsequent filtering, resulting in a significantly brighter and more readily usable quantum state. The team achieves this by carefully controlling the interaction between photons within a nonlinear medium, effectively ‘shaping’ the quantum state into a desired non-Gaussian form. This deterministic generation represents a substantial advancement, paving the way for more practical and efficient quantum technologies by providing a robust source of complex quantum states.

Husimi Function Maps Kerr Nonlinearity in Light

Scientists engineered a method to deterministically generate a bright, non-Gaussian state of light by introducing a Kerr nonlinearity to bright squeezed vacuum (BSV). The study pioneered the use of a single-shot interferometer to sample the Husimi function, a statistical representation of the light’s quantum state, allowing detailed characterization of the generated non-Gaussian state. Experiments revealed a clear transformation from an initial two-dimensional Gaussian distribution to a characteristic ‘S’-shaped non-Gaussian profile, providing direct statistical evidence of the intensity-dependent nonlinear phase induced by the Kerr effect. To theoretically describe the observed large-scale structure of the Husimi function, researchers employed the classical Liouville equation, demonstrating that the Kerr nonlinearity effectively induces a phase-space rotation proportional to the squared distance from the origin.

This amplitude-dependent shear transforms the initially elongated Gaussian Husimi function of BSV into the characteristic ‘S’-shaped profile. The team carefully controlled the experimental setup, observing that at higher intensities, competing nonlinear processes depleted the high-photon-number components of the BSV state, resulting in a ‘cut-off’ in the measured distribution. The study further investigated the composition of BSV, demonstrating that it can be effectively modeled as a mixture of pure squeezed coherent states. Scientists calculated that even minute optical losses significantly reduce the purity of the BSV state.

Despite these losses, the minimal variance of the BSV quadratures remained below the vacuum level, preserving its non-classical character. Researchers mathematically showed that after experiencing loss, BSV transforms into a squeezed thermal state, describable as a mixture of squeezed coherent states, with the squeezing parameter and effective photon number determined by the initial conditions and the amount of loss. This mixture of states is stochastically displaced in phase space, leading to quantum decoherence, but importantly, some components retain significant squeezing along a single quadrature. Finally, the team simulated the effect of the Kerr nonlinearity on these individual squeezed states, revealing that phase-squeezed states exhibit a pronounced Wigner-function negativity, even under weak Kerr action, demonstrating the potential for generating strongly non-Gaussian states within the BSV mixture.

Kerr Effect Alters Squeezed Vacuum States

This research demonstrates the deterministic generation of a bright, non-Gaussian state of light by introducing a Kerr nonlinearity to a bright squeezed vacuum (BSV). Scientists achieved this transformation by manipulating the phase of light within a nonlinear material, resulting in a measurable shift from a Gaussian to an ‘S’-shaped distribution when sampling the Husimi function. This represents a significant step towards creating robust quantum states suitable for advanced applications. The team characterized the resulting state using a single-shot interferometer, confirming the nonlinear phase shift and demonstrating that BSV, while typically a mixed state susceptible to loss, can be understood as a combination of purer squeezed coherent states.

Although direct observation of Wigner function negativity, a hallmark of non-Gaussian states, was limited by experimental loss, the research establishes that BSV retains quantum superposition characteristics even with realistic levels of optical loss. The findings bridge the fields of optics and ultrafast nonlinear optics, paving the way for applications requiring high photon flux. The authors acknowledge that the purity of BSV is sensitive to loss from optical components and the nonlinear material itself. Future research directions include adopting purification protocols currently used for Gaussian states and developing new methods leveraging strong-field light-matter interactions. These advancements promise to further isolate pure squeezed coherent states and unlock the potential for exploring quantum dynamics beyond current limitations.

Bright Squeezed States via Kerr Nonlinearity

This research demonstrates the deterministic generation of a bright, non-Gaussian state of light by introducing a Kerr nonlinearity to a bright squeezed vacuum (BSV). Scientists achieved this transformation by manipulating the phase of light within a nonlinear material, resulting in a measurable shift from a Gaussian to an ‘S’-shaped distribution when sampling the Husimi function. This represents a significant step towards creating robust quantum states suitable for advanced applications. The team characterized the resulting state using a single-shot interferometer, confirming the nonlinear phase shift and demonstrating that BSV, while typically a mixed state susceptible to loss, can be understood as a combination of purer squeezed coherent states.

Although direct observation of Wigner function negativity, a hallmark of non-Gaussian states, was limited by experimental loss, the research establishes that BSV retains quantum superposition characteristics even with realistic levels of optical loss. The findings bridge the fields of optics and ultrafast nonlinear optics, paving the way for applications requiring high photon flux. The authors acknowledge that the purity of BSV is sensitive to loss from optical components and the nonlinear material itself. Future research directions include adopting purification protocols currently used for Gaussian states and developing new methods leveraging strong-field light-matter interactions. These advancements promise to further isolate pure squeezed coherent states and unlock the potential for exploring quantum dynamics beyond current limitations.