Observation of squeezed light with 10dB quantum noise reduction (0706.1431v1)

Abstract: Squeezing of light's quantum noise requires temporal rearranging of photons. This again corresponds to creation of quantum correlations between individual photons. Squeezed light is a non-classical manifestation of light with great potential in high-precision quantum measurements, for example in the detection of gravitational waves. Equally promising applications have been proposed in quantum communication. However, after 20 years of intensive research doubts arose whether strong squeezing can ever be realized as required for eminent applications. Here we show experimentally that strong squeezing of light's quantum noise is possible. We reached a benchmark squeezing factor of 10 in power (10dB). Thorough analysis reveals that even higher squeezing factors will be feasible in our setup.

• The paper demonstrates a 10.12 dB quantum noise reduction in squeezed light, surpassing previous benchmarks in precision measurements.
• It employs a monolithic Nd:YAG ring laser and type I degenerate optical parametric oscillation with travelling-wave resonators to effectively minimize phase noise.
• This breakthrough paves the way for enhanced gravitational wave detection and robust quantum communication by significantly boosting measurement sensitivity.

Observation of Squeezed Light with 10 dB Quantum Noise Reduction: A Technical Analysis

The paper "Observation of squeezed light with 10 dB quantum noise reduction" by Vahlbruch et al. presents an experimental demonstration of achieving 10 dB reduction in the quantum noise of light using squeezed states. The work focuses on overcoming longstanding skepticism about the feasibility of generating strong squeezed light, which is essential for advancing high-precision quantum measurements and quantum communication.

Summary of the Research

The concept of squeezed light, introduced in the early 20th century but explored in depth since the 1980s, involves reducing quantum noise in one quadrature of light at the expense of increased noise in the orthogonal quadrature. This reduction in noise is desirable for applications such as enhancing the sensitivity of laser interferometers used in gravitational wave detection and for continuous-variable (CV) quantum communication systems. Prior to this work, the highest reported squeezing factor was about 9 dB, achieved using a laser source close to atomic transitions.

The experiment conducted by Vahlbruch et al. employs a monolithic non-planar Nd:YAG ring laser at 1064 nm, a wavelength relevant to current gravitational wave detectors. The experimental setup involves generating squeezed light through type I degenerate optical parametric oscillation (OPO) using a MgO:LiNbO₃ crystal. Their optimized setup utilizes high-stability resonators to filter phase noise and achieves a squeezing level of 10.12 dB as measured at a 5 MHz Fourier frequency.

Key Technical Achievements

1. Quantum Noise Reduction: The experiment successfully achieves a direct observation of 10.12 dB squeezing, surpassing previous benchmarks. This represents a substantial reduction in the quantum noise, a notable achievement given the historical challenges in pushing beyond 6 dB.
2. Elimination of Phase Fluctuations: The use of travelling-wave resonators minimizes phase noise, a critical hurdle in previous experiments. This enabled the observed strong squeezing by mitigating noise that could otherwise couple with anti-squeezing effects.
3. Optical Setup Stability: The setup's stability obviates the need for servo-loop control of the laser frequency. The precise mode matching and thermal stabilization of the squeezing source are crucial for maintaining high squeezing levels.
4. Detection Efficiency: The homodyne detection system exhibits a high fringe visibility (99.8%), and the dark noise is significantly lower than the quantum noise level, underscoring the system's reliability in measuring squeezed states.

Implications and Future Directions

The achievement of 10 dB noise reduction confirms the viability of using squeezed light for applications historically deemed impractical due to insufficient squeezing levels. For gravitational wave detectors, this implies potentially increasing their sensitivity without resorting to unfeasibly high laser power.

Looking forward, improvements in photodiode quantum efficiency and reduction of optical losses may further enhance squeezing levels. This could enable a broader range of applications, including more robust quantum communication protocols and enhanced quantum key distribution schemes. Furthermore, stronger squeezed states could allow for the generation of highly entangled states suitable for teleportation with high fidelity, exceeding the classical fidelity limits.

Vahlbruch et al.'s work sets a new standard in the field of quantum optics and opens avenues for both theoretical exploration and practical application of squeezed light in quantum technologies. As researchers continue to optimize optical setups and reduce losses, the integration of squeezed light into existing quantum systems seems imminent, promising significant advancements in both fundamental physics and applied quantum technology.