2020-09-18 Abstract
Title: When Quantum Noise meets General Relativity
Speaker: Ray-Kuang Lee (National Tsing Hua University)
Date: September 18 at 14:30
Location: R521, General Building II
Abstract:
The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. To "hear" the black holes, gravitational-wave astronomy uses gravitational-waves detectors to collect observational data from binary star systems composed of black holes (and neutron stars). However, the astrophysical reach of current and future ground-based gravitational-wave detectors is mostly limited by the quantum noise, induced by vacuum fluctuations entering the detector output port. Even though a quantum state, as well as its wavefunction, is a mathematical entity in quantum physics, the knowledge of the quantum state makes the quantum information science accessible. Based on the Wigner function in phase space [1], I will report our implementation of squeezed vacuum states at 1064 nm, with the noise reduction up to 10dB below the vacuum fluctuations. Based on the convolutional neural network (CNN) used in machine learning [2], we demonstrate experimentally a fast reconstruction of quantum wavefunction to "see" the corresponding density matrix elements for continuous variables quantum states. In addition to the measurement scheme based on our home-made balanced homodyne detectors, the weak measurement theory can also provide an alternative approach to enhance the measured values [3]. Applications of our squeezer to the gravitational-wave detection will be demonstrated, for the first demonstration of a frequency dependent squeezed vacuum source able to reduce quantum noise of advanced gravitational-wave detectors in their whole observation bandwidth. The experiment uses a suspended 300 m long filter cavity at National Astronomical Observatory of Japan (NAOJ), similar to the one planned for KAGRA, Advanced Virgo and Advanced LIGO, and capable to impress a rotation of the squeezing ellipse below 100 Hz [4].
[1] Popo Yang, Ivan F. Valtierra, Andrei B. Klimov, Shin-Tza Wu, RKL, and Luis L. Sanchez-Soto, and Gerd Leuchs, "The Wigner flow on the sphere," Physica Scripta 94, 044001 (2019); for the New Focus issue: Quantum Optics and Beyond- in honour of Wolfgang Schleich.
[2] Alexey A. Melonikov, Leonid E. Fedichkin, RKL, and Alexander Alodjants, "Machine learning transfer efficiencies for noisy quantum walks," Adv. Quant. Tech. 3,1900115 (2020); also selected as the Back Cover for Adv. Quant. Tech. April issue (2020).
[3] Minyi Huang, RKL, Lijian Zhang, Shao-Ming Fei, and Junde Wu, "Simulating broken PT-symmetric Hamiltonian systems by weak measurement," Phys. Rev. Lett. 123, 080404 (2019).
[4] Yuhang Zhao et al., "Frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors," Phys. Rev. Lett. 124, 171101 (2020); Editors' Suggestion; Featured in Physics.