Plasma Waves Enable Ultra-Strong Squeezed States for High-Photon Number Applications

Quantum squeezing enhances the precision of measurements beyond conventional limits, but current technologies using solid materials restrict the power of the squeezing process. Kenan Qu, Nathaniel J. Fisch, and colleagues at Princeton University demonstrate a new method using plasma waves to achieve remarkably strong quantum squeezing. The team shows that by carefully controlling laser beams interacting with plasma, they can generate highly correlated pairs of photons through a process involving stimulated Raman scattering and four-wave mixing. This innovative approach overcomes limitations of traditional methods, exhibiting resilience to thermal noise and enabling the creation of squeezed states with an exceptionally high number of photons, which promises significant advances in strong-field applications ranging from visible light to X-ray wavelengths.

Squeezed Light Intensity and Frequency Limitations

Quantum squeezed states represent a fundamental advance in precision measurement, allowing for the reduction of quantum noise below the standard limit and enhancing the sensitivity of applications like gravitational wave detection and quantum imaging. Achieving these enhancements, however, requires access to squeezed light with extreme intensity or frequency, regimes that remain challenging with existing generation methods. Current production methods are limited by the material properties of solid-state media, which exhibit low damage thresholds and restrict operation to the optical-to-infrared spectral range. Overcoming this barrier necessitates moving to ionized plasma media, where pump powers can exceed solid-state limits.

While early studies involving laser-plasma interactions were limited, recent advances in attosecond physics have demonstrated the generation of nonclassical light. Fully ionized plasmas eliminate ionization constraints, enabling pump intensities exceeding 10 16 Wcm -2 while supporting efficient nonlinear interactions. Recent work demonstrated the feasibility of achieving 20 dB squeezing via plasma-based relativistic four-wave mixing, but this process is susceptible to classical noise sources. The team now presents a superior approach using stimulated Raman scattering, a first-order process with dramatically higher growth rates that eliminates primary classical noise sources while enabling unprecedented squeezing levels.

This innovation employs phonon-mediated four-wave mixing, where plasma Langmuir waves act as quantum intermediaries between optical modes, producing quantum-correlated photon pairs with exceptional robustness to thermal noise. The process involves two distinct SRS processes, generating ideal two-mode squeezed states. Specifically, a pump photon converts into a photon at the Stokes sideband by creating a phonon, which is quantum-correlated with the emitted photon. Replacing this intermediate phonon with a second optical photon via the anti-Stokes process, where a pump photon is converted into a photon at the anti-Stokes sideband by absorbing a phonon, allows for isolation of quantum-correlated noise using interference. This is analyzed using a Bogoliubov transformation, defining two hybrid modes that form a two-mode squeezed vacuum state. The team’s results indicate that a large thermal phonon number can be overcome at the cost of a reduced coupling rate and a longer laser-plasma interaction region.

Plasma Pulse Generation and Quantum State Control

Methods for generating and manipulating light pulses in plasmas have been extensively researched, building upon established principles and exploring novel approaches. The research explores how quantum states can be created and manipulated in extreme conditions, like those found in high-harmonic generation and plasma interactions, with a central goal of leveraging these techniques for applications in quantum technologies. Established techniques like optical parametric oscillators, high-harmonic generation, and superradiant amplification are being investigated for creating squeezed light and even more complex quantum states like Schrödinger cat states. The abstract emphasizes the importance of understanding the quantum optical nature of these processes, focusing on controlling the squeezing, entanglement, and coherence of light.

This research could lead to new tools for quantum computing, sensing, and communication. Squeezed light, a non-classical state where quantum fluctuations are reduced, is crucial for improving the sensitivity of measurements and reducing noise in quantum technologies. The research also investigates the potential of semiconductor materials for generating squeezed light, potentially offering compact and efficient quantum light sources. Understanding quantum optics, non-classical light, and superradiance is essential for advancing these technologies. This research proposes alternative methods for generating squeezed light that could be more compact, efficient, or versatile than existing techniques, bridging quantum optics and strong-field physics. The ability to generate and control squeezed light is essential for many quantum technologies, and this research could pave the way for new breakthroughs. The research contributes to a deeper understanding of the quantum nature of light-matter interactions, crucial for developing new technologies and advancing our knowledge of the physical world.

Squeezed Light from Laser-Matter Interactions

This research demonstrates a novel method for generating squeezed states of light using plasma waves, achieving ultra-strong squeezing intensities previously unattainable with conventional solid-state materials. By employing two co-propagating pump beams and leveraging stimulated Raman scattering, the team successfully generated correlated photon pairs, exhibiting remarkable resilience to thermal noise even with substantial thermal phonon numbers. This approach overcomes limitations imposed by ionization thresholds in traditional media, enabling the production of squeezed states with significantly higher photon numbers. The findings open new possibilities for applications requiring precision measurements and strong-field interactions, potentially extending to the X-ray wavelength range. While the study highlights the robustness of the method, the authors acknowledge that further investigation is needed to fully characterize the process and optimize its efficiency. Future work could focus on exploring different plasma conditions and pump beam configurations to enhance squeezing levels and broaden the range of achievable wavelengths, ultimately paving the way for advanced technologies in fields like quantum optics and high-resolution imaging.