Quantum process tomography, as an advanced means of metrology, has a capacious range of applications for estimating numerous meaningful parameters. The parameter estimate precision of using coherent state and single photon state as probe are limited by the shot noise limit. Here we demonstrate a quantum enhanced rotating angle measure scheme based on the four-photon Holland-Burnett state can achieve the Heisenberg scaling by the coincidence counting technology. At the same time, the output signal of our scheme has an 8-fold super-resolution compared to the Malus law. In addition, the accuracy achieved by four photons is consistent with using 12 photons of single photon probe. That has incomparable preponderance in a situation in which only weak light can be exploited, like the measure of frangible biological specimens and photosensitive crystals. Moreover, the four-photon Holland-Burnett state can be generated by a polarization-entangled light source. These ensure that our scheme has a champaign application prospect.
The polarization of the light is an excellent information carrier, but polarization information of coherent state in the quantum measurement of the past has not been clearly expressed. We refer to some ideas of quantum computation and quantum information, considering the polarization mode of the electromagnetic field to describe polarization information of a coherent state. And on this basis we put forward a polarization rotation angle measurement device based on a Mach-Zehnder interferometer and two polarizers. We also consider the intensity detection, parity detection and Z detection as detection strategies. The results show that this device can realize the super-resolution and shot noise limit with parity detection and Z detection. By simulation analysis, we finally find parity detection is the best method for our scheme, and we also discuss the effects of some parameters on sensitivity and resolution with parity detection.
Lidar based on Geiger-mode Avalanche Photodiode Detector (Gm-APD), also called Gm-APD Lidar for short, has the advantages of the ultra-high sensitivity and ranging accuracy, and therefore it is widely used in the weak signal detection over a long distance. Time-Correlated Single Photon Counting (TCSPC) is a more commonly used signal processing method of Gm-APD Lidar. However, after each avalanche response, Gm-APD needs a certain time to quench avalanche current, which is called the dead time. In the dead time, Gm-APD can't response any signal. This will result in the uneven response by Gm-APD, and the response probability of the front of the echo pulse signal is higher than that of the back of the echo pulse signal. The peak of photon counting results will deviate from the real peak of the echo signal, and this deviation will become larger with the increase of the echo pulse width. In many application environments (for example, underwater, battlefield smoke, fog and dust, etc.), the broadening effect of the echo pulse signal is obvious, and this will seriously impact the ranging accuracy of Gm-APD Lidar. In this paper, an improved method uses the multi-gate detection to response the complete waveform of the echo pulse signal, and thus improves the ranging accuracy of GmAPD due to obtaining more accurate echo pulse peak.
We propose a novel strategy of asymmetric triangular-wave modulation for photon-counting chirped amplitude
modulation (PCCAM) lidar. Earlier studies use the symmetric triangle wave modulation, by which the velocity can be
detected only when the Doppler shift caused by a moving target is greater than Full Width Half Maximum (FWHM) of
Intermediate Frequency (IF). We use an alternative method known as the asymmetric triangular wave modulation
method, in which the modulation rates of the up-ramp and the down-ramp are different. This new method avoids the
overlapping of the up-ramp and the down-ramp IF peaks, and breaks the limit of the FWHM of IF peak to improve the
velocity measuring sensitivity (also called the minimum detectable velocity). Finally, a proof-of-principle experiment is
carried out in the laboratory. The experimental results agree well with the theoretical results and show the improvement
of the minimum detectable velocity.
Since Geiger mode Avalanche Photodiode (GmAPD) device was applied in laser radar system, the performance of
system has been enhanced due to the ultra-high sensitivity of GmAPD, even responding a single photon. However, the
background noise makes ultra-high sensitive GmAPD produce false alarms, which severely impacts on the detection of
laser radar system based on Gm-APD and becomes an urgent problem which needs to be solved. To address this
problem, a few times accumulated two-GmAPDs strategy is proposed in this paper. Finally, an experimental
measurement is made under the background noise in sunny day. The results show a few times accumulated two-
GmAPDs strategy can improve the detection probability and reduce the false alarm probability, and obtain a clear 3D
image of target.