High-Q coupled resonances on a PhC waveguide using a tapered nanofiber with high coupling efficiency

We experimentally demonstrate high-Q cavity formation at an arbitrary position on a silicon photonic crystal waveguide by bringing a tapered nanofiber into contact with the surface of the slab. An ultrahigh Q of 5.1 x 10^5 is obtained with a coupling efficiency of 39%, whose resonant wavelength can be finely tuned by 27 pm by adjusting the contact length of the nanofiber. We also demonstrate an extremely high coupling efficiency of 99.6% with a loaded Q of 6.1 x 10^3. In addition, we show that we can obtain an all-pass filter type coupled resonator system, which has the potential to be used for slow light generation.Comment: 8 pages, 7 figures. The following article has been submitted to Optics Express. After it is published, it will be found at https://www.osapublishing.org/oe/home.cf

Axion Dark Matter Search with Interferometric Gravitational Wave Detectors

Axion dark matter differentiates the phase velocities of the circular-polarized photons. In this Letter, a scheme to measure the phase difference by using a linear optical cavity is proposed. If the scheme is applied to the Fabry-P\'erot arm of Advanced LIGO-like (Cosmic-Explorer-like) gravitational wave detector, the potential sensitivity to the axion-photon coupling constant, $g_{\text{a}\gamma}$, reaches $g_{\text{a}\gamma} \simeq 8\times10^{-13}$ GeV$^{-1}\, (4 \times 10^{-14}$ GeV$^{-1})$ at the axion mass $m \simeq 3\times 10^{-13}$ eV ($2\times10^{-15}$ eV) and remains at around this sensitivity for 3 orders of magnitude in mass. Furthermore, its sensitivity has a sharp peak reaching $g_{\text{a}\gamma} \simeq 10^{-14}$ GeV$^{-1}$ $(8\times10^{-17}$ GeV$^{-1})$ at $m = 1.563\times10^{-10}$ eV ($1.563\times10^{-11}$ eV). This sensitivity can be achieved without loosing any sensitivity to gravitational waves.Comment: 7 pages, 2 figure

Improved sensitivity of interferometric gravitational wave detectors to ultralight vector dark matter from the finite light-traveling time

Recently several studies have pointed out that gravitational-wave detectors are sensitive to ultralight vector dark matter and can improve the current best constraints given by the Equivalence Principle tests. While a gravitational-wave detector is a highly precise measuring tool of the length difference of its arms, its sensitivity is limited because the displacements of its test mass mirrors caused by vector dark matter are almost common. In this Letter we point out that the sensitivity is significantly improved if the effect of finite light-traveling time in the detector's arms is taken into account. This effect enables advanced LIGO to improve the constraints on the $U(1)_{B-L}$ gauge coupling by an order of magnitude compared with the current best constraints. It also makes the sensitivities of the future gravitational-wave detectors overwhelmingly better than the current ones. The factor by which the constraints are improved due to the new effect depends on the mass of the vector dark matter, and the maximum improvement factors are $470$, $880$, $1600$, $180$ and $1400$ for advanced LIGO, Einstein Telescope, Cosmic Explorer, DECIGO and LISA respectively. Including the new effect, we update the constraints given by the first observing run of advanced LIGO and improve the constraints on the $U(1)_B$ gauge coupling by an order of magnitude compared with the current best constraints.Comment: 6 pages, 3 figure

Ultralight vector dark matter search with auxiliary length channels of gravitational wave detectors

Recently, a considerable amount of attention has been given to the search for ultralight dark matter by measuring the oscillating length changes in the arm cavities of gravitational wave detectors. Although gravitational wave detectors are extremely sensitive for measuring the differential arm length changes, the sensitivity to dark matter is largely attenuated, as the effect of dark matter is mostly common to arm cavity test masses. Here, we propose to use auxiliary length channels, which measure the changes in the power and signal recycling cavity lengths and the differential Michelson interferometer length. The sensitivity to dark matter can be enhanced by exploiting the fact that auxiliary interferometers are more asymmetric than two arm cavities. We show that the sensitivity to $U(1)_{B-L}$ gauge boson dark matter with masses below $7\times 10^{-14}$ eV can be greatly enhanced when our method is applied to a cryogenic gravitational wave detector KAGRA, which employs sapphire test masses and fused silica auxiliary mirrors. We show that KAGRA can probe more than an order of magnitude of unexplored parameter space at masses around $1.5 \times 10^{-14}$ eV, without any modifications to the existing interferometer.Comment: 6 pages, 3 figure

Axion dark matter search using arm cavity transmitted beams of gravitational wave detectors

Axion is a promising candidate for ultralight dark matter which may cause a polarization rotation of laser light. Recently, a new idea of probing the axion dark matter by optical linear cavities used in the arms of gravitational wave detectors has been proposed [Phys. Rev. Lett. 123, 111301 (2019)]. In this article, a realistic scheme of the axion dark matter search with the arm cavity transmission ports is revisited. Since photons detected by the transmission ports travel in the cavity for odd-number of times, the effect of axion dark matter on their phases is not cancelled out and the sensitivity at low-mass range is significantly improved compared to the search using reflection ports. We also take into account the stochastic nature of the axion field and the availability of the two detection ports in the gravitational wave detectors. The sensitivity to the axion-photon coupling, $g_{a\gamma}$, of the ground-based gravitational wave detector, such as Advanced LIGO, with 1-year observation is estimated to be $g_{a\gamma} \sim 3\times10^{-12}$ GeV$^{-1}$ below the axion mass of $10^{-15}$ eV, which improves upon the limit achieved by the CERN Axion Solar Telescope.Comment: 10 pages, 4 figure