Zebing Zhou

TianQin: a space-borne gravitational wave detector

TianQin is a proposal for a space-borne detector of gravitational waves in the millihertz frequencies. The experiment relies on a constellation of three drag-free spacecraft orbiting the Earth. Inter-spacecraft laser interferometry is used to monitor the distances between the test masses. The experiment is designed to be capable of detecting a signal with high confidence from a single source of gravitational waves within a few months of observing time. We describe the preliminary mission concept for TianQin, including the candidate source and experimental designs. We present estimates for the major constituents of the experiments error budget and discuss the projects overall feasibility. Given the current level of technology readiness, we expect TianQin to be flown in the second half of the next decade.

A scientific case study of an advanced LISA mission

A brief status report of an ongoing scientific case study of the Advanced Laser Interferometer Antenna (ALIA) mission is presented. Key technology requirements and primary science objectives of the mission are covered in the study. Possible descope options for the mission and the corresponding compromise in science are also considered and compared. Our preliminary study indicates that ALIA holds promise in mapping out the mass and spin distribution of intermediate mass black holes possibly present in dense star clusters at low redshift as well as in shedding important light on the structure formation in the early Universe.

Low-frequency seismic spectrum measured by a laser interferometer combined with a low-frequency folded pendulum

Al aser interferometer combined with a reference mirror suspended on a long-period folded pendulum is presented to measure the low-frequency horizontal seismic spectrum. One of the reflecting mirrors is driven by a piezoelectric transducer to track another mirror. The experimental results show that the horizontal seismic motion is about 10 −9 mH z −1/2 at 1 Hz in

Null result for violation of the equivalence principle with free-fall rotating gyroscopes

The differential acceleration between a rotating mechanical gyroscope and a nonrotating one is directly measured by using a double free-fall interferometer, and no apparent differential acceleration has been observed at the relative level of 2 x 10(-6). It means that the equivalence principle is still valid for rotating extended bodies, i.e., the spin-gravity interaction between the extended bodies has not been observed at this level. Also, to the limit of our experimental sensitivity, there is no observed asymmetrical effect or antigravity of the rotating gyroscopes as reported by Hayasaka et al.

Descope of the ALIA mission

The present work reports on a feasibility study commissioned by the Chinese Academy of Sciences of China to explore various possible mission options to detect gravitational waves in space alternative to that of the eLISA/LISA mission concept. Based on the relative merits assigned to science and technological viability, a few representative mission options descoped from the ALIA mission are considered. A semi-analytic Monte Carlo simulation is carried out to understand the cosmic black hole merger histories starting from intermediate mass black holes at high redshift as well as the possible scientific merits of the mission options considered in probing the light seed black holes and their coevolution with galaxies in early Universe. The study indicates that, by choosing the armlength of the interferometer to be three million kilometers and shifting the sensitivity floor to around one-hundredth Hz, together with a very moderate improvement on the position noise budget, there are certain mission options capable of exploring light seed, intermediate mass black hole binaries at high redshift that are not readily accessible to eLISA/LISA, and yet the technological requirements seem to within reach in the next few decades for China.

High resolution space quartz-flexure accelerometer based on capacitive sensing and electrostatic control technology

High precision accelerometer plays an important role in space scientific and technical applications. A quartz-flexure accelerometer operating in low frequency range, having a resolution of better than 1 ng/Hz(1/2), has been designed based on advanced capacitive sensing and electrostatic control technologies. A high precision capacitance displacement transducer with a resolution of better than 2 × 10(-6) pF/Hz(1/2) above 0.1 Hz, is used to measure the motion of the proof mass, and the mechanical stiffness of the spring oscillator is compensated by adjusting the voltage between the proof mass and the electrodes to induce a proper negative electrostatic stiffness, which increases the mechanical sensitivity and also suppresses the position measurement noise down to 3 × 10(-10) g/Hz(1/2) at 0.1 Hz. A high resolution analog-to-digital converter is used to directly readout the feedback voltage applied on the electrodes in order to suppress the action noise to 4 × 10(-10) g/Hz(1/2) at 0.1 Hz. A prototype of the quartz-flexure accelerometer has been developed and tested, and the preliminary experimental result shows that its resolution comes to about 8 ng/Hz(1/2) at 0.1 Hz, which is mainly limited by its mechanical thermal noise due to low quality factor.

Performance measurements of an inertial sensor with a two-stage controlled torsion pendulum

A novel two-stage electrostatically controlled torsion pendulum has been developed to simultaneously investigate the performance of a translational and a rotational degree of freedom of an electrostatic inertial sensor on ground. The motions of the proof mass (PM) relative to the electrode frame are monitored by a high-precision capacitance transducer, and are synchronously controlled by electrostatic actuators. The parasitic stiffness induced by capacitance transducers and the effect of the magnetic field are measured. Both translational and rotational motions of the PM succeed to be simultaneously controlled, and the cross-coupling effect between both controlled degrees of freedom is also preliminary measured. The experiments show that the scheme obviously suppresses the translational to rotational effect of the PM, and then effectively improves the torque resolution compared with the single-stage torsion pendulum. The noise floors of the controlled torsion pendulum come to 1.2 × 10 −11 NH z −1/2 along the translational degree of freedom, and 1.4 × 10 −13 NmH z −1/2 along the rotational degree of freedom, near 30 mHz, which are mainly limited by the back action of the capacitance transducer below 0.1 Hz and by the horizontal seismic noise disturbance above 0.1 Hz.

New upper limit from terrestrial equivalence principle test for extended rotating bodies

An improved terrestrial experiment to test the equivalence principle for rotating extended bodies is presented, and a new upper limit for the violation of the equivalence principle is obtained at the level of 1.6x10(-7), which is limited by the friction of the rotating gyroscope. This means that the spin-gravity interaction between the extended bodies has not been observed at this level.

Resonant frequency detection and adjustment method for a capacitive transducer with differential transformer bridge

The capacitive transducer with differential transformer bridge is widely used in ultra-sensitive space accelerometers due to their simple structure and high resolution. In this paper, the front-end electronics of an inductive-capacitive resonant bridge transducer is analyzed. The analysis result shows that the performance of this transducer depends upon the case that the AC pumping frequency operates at the resonance point of the inductive-capacitive bridge. The effect of possible mismatch between the AC pumping frequency and the actual resonant frequency is discussed, and the theoretical analysis indicates that the output voltage noise of the front-end electronics will deteriorate by a factor of about 3 due to either a 5% variation of the AC pumping frequency or a 10% variation of the tuning capacitance. A pre-scanning method to determine the actual resonant frequency is proposed followed by the adjustment of the operating frequency or the change of the tuning capacitance in order to maintain expected high resolution level. An experiment to verify the mismatching effect and the adjustment method is provided.

Torsion pendulum for the performance test of the inertial sensor for ASTROD-I

A torsion pendulum facility for a ground-based performance test of the inertial sensor for ASTROD-1 has been constructed. The twist motion of the test mass is monitored and servo-controlled. The sensitivity of the electrostatic servo-controlled actuator is calibrated based on the elastic torque of the torsion fibre, and the torque resolution of the servo-controlled torsion pendulum comes to 2 × 10−11 N m Hz−1/2 from 1 mHz to 0.1 Hz, which is likely limited by the seismic noise, electronic noise and the cross coupling between the translation and twist modes.