12.6 dB squeezed light at 1550 nm from a bow-tie cavity for long-term high duty cycle operation*

Squeezing has numerous applications in metrology, secure quantum communication, and continuous variable quantum information protocols. One of the most notable applications of squeezed light is in gravitational wave sensing , where it is used to improve sensitivity. The Einstein Telescope, a next-generation gravitational wave detector, will require squeezed light with a quantum noise suppression of 10 dB. Squeezing is also essential for continuous variable quantum information protocols, such as quantum teleportation, cluster states, and heralded gates. The squeezing requirement for nominal logical error rates in fault-tolerant measurement based quantum computing is 11.9 dB. A key challenge is to develop squeezers that offer very high squeezing levels while maintaining high duty cycles and operating at room temperature while ensuring the design is accessible to the community at large. By using modified coherent lock and carefully designing the optomechanics of the bowtie squeezing cavity, we were able to achieve this. The bowtie design is a versatile platform that does not require highly customized crystals, as is otherwise employed in the design of monolithic or hemilithic designs. We demonstrate that through careful design and suitable control schemes, the bowtie cavity is capable of producing high squeezing levels with good temporal stability, which makes it suitable for post selection based continuous-variable quantum information protocols, cluster-state quantum computing, quantum metrology, and potentially gravitational wave detectors. Over 50 hours of continuous operation, the measured squeezing levels were greater than 10 dB with a duty cycle of 96.6%. This was facilitated through the use of an automated control/relock system. Alternatively, we also use an active compensation control system to demonstrate the continuous operation of the squeezer over a 12-hour period with no relocks, with an average squeezing of 11.9 dB that meets the squeezing requirement for fault-tolerant measurement-based quantum computing. We also measured a maximum squeezing level of 12.6 dB at 1550 nm, which represents one of the best reported squeezing results at 1550 nm to date for a bow-tie cavity.