Same Wavelength Noise Filtering via Quantum Orbital Angular Momentum Emission.

In laser active detection, detection performance is affected by optical noise, laser interference, and environmental background interference. Conventional methods to filter optical noise take advantage of the differences between signal and noise in wavelength and polarization. Due to the limitations of traditional methods in the physical dimension, noise cannot be completely filtered out. In this manuscript, a new method of noise filtering based on the spatial distribution difference between the quantum orbital angular momentum beam and the background noise is proposed. The use of beams containing quantum orbital angular momentum can make the signal light have a new physical dimension and enrich the information of emitted light. We conduct a complete theoretical analysis and provide a proof-of-principle experiment. The experimental results are in good agreement with the theoretical analysis results, and there is a signal-to-noise ratio improvement of more than five times in laser active detection. Our method meets the urgent needs of laser active detection and can be applied in the field of high-quality target detection.

Prediction of the Number of Cumulative Pulses Based on the Photon Statistical Entropy Evaluation in Photon-Counting LiDAR.

Photon-counting LiDAR encounters interference from background noise in remote target detection, and the statistical detection of the accumulation of multiple pulses is necessary to eliminate the uncertainty of responses from the Geiger-mode avalanche photodiode (Gm-APD). The cumulative number of statistical detections is difficult to select due to the lack of effective evaluation of the influence of the background noise. In this work, a statistical detection signal evaluation method based on photon statistical entropy (PSE) is proposed by developing the detection process of the Gm-APD as an information transmission model. A prediction model for estimating the number of cumulative pulses required for high-accuracy ranging with the background noise is then established. The simulation analysis shows that the proposed PSE is more sensitive to the noise compared with the signal-to-noise ratio evaluation, and a minimum PSE exists to ensure all the range detections with background noise are close to the true range with a low and stable range error. The experiments demonstrate that the prediction model provides a reliable estimation of the number of required cumulative pulses in various noise conditions. With the estimated number of cumulative pulses, when the signal photons are less than 0.1 per pulse, the range accuracy of 4.1 cm and 5.3 cm are obtained under the background noise of 7.6 MHz and 5.1 MHz, respectively.

Tiny velocity measurement using rotating petal-like mode of orbital angular momentum.

A novel, to the best of our knowledge, tiny velocity measurement system is proposed and demonstrated. This proposed system employs an interference structure in which the reference and measurement paths are filled by two light beams carrying opposite-sign orbital angular momentum (OAM), respectively. The tiny velocity to be measured in the measurement path causes the change of the light path and results in a time-varying phase shift between the reference and measurement paths. This time-varying phase shift leads to the rotation of the petal-like light spot obtained by the interference between two paths. The rotating angular velocity of the petal-like light spot is proportional to the time-varying phase shift caused by the tiny velocity, and it is measured by a chopper and a single-point detector instead of array detectors. This proposed system has a simple structure and achieves a high-accuracy tiny velocity measurement with a measurement error rate that is less than 10 nm/s.

Rotation velocity detection with orbital angular momentum light spot completely deviated out of the rotation center.

Based on the rotational Doppler effect, an orbital angular momentum beam can measure the lateral rotation velocity of an object, which has broad application prospects. However, all existing research focus on the light spot center coinciding with the rotation center, or only with small center offset. This is difficult to ensure in remote detection applications. In this paper, the rotational Doppler frequency shifts under three cases, including no center offset, small center offset and large center offset, are analyzed theoretically. Through theoretical research results, a novel method of measuring rotation velocity is proposed, with the light spot completely deviated out of the rotation center. A laboratory verification experiment shows that this proposed method breaks the limit of center offset of lateral rotation velocity measurement and is of great significance to the remote detection of non-cooperative rotation object.

Super-resolved angular displacement estimation based upon a Sagnac interferometer and parity measurement.

Super-resolved angular displacement estimation is of crucial significance to the field of quantum information processing. Here we report an estimation protocol based on a Sagnac interferometer fed by a coherent state carrying orbital angular momentum. In a lossless scenario, through the use of parity measurement, our protocol can achieve a 4ℓ-fold super-resolved output with quantum number ℓ; meanwhile, a shot-noise-limited sensitivity saturating the quantum Cramér-Rao bound is reachable. We also consider the effects of several realistic factors, including nonideal state preparation, photon loss, and inefficient measurement. Finally, with mean photon number N¯=2.297 and ℓ = 1 taken, we experimentally demonstrate a super-resolved effect of angular displacement with a factor of 7.88.

Tried-and-true binary strategy for angular displacement estimation based upon fidelity appraisal.

We demonstrate a tried-and-true binary strategy for angular displacement estimation, of which the measuring system is a modified Mach-Zehnder interferometer fed by a coherent state carrying orbital angular momentum, and two Dove prisms are embedded in two arms. Unlike previous protocols, in this paper, we use fidelity instead of standard deviation to evaluate the detection strategies. Two binary strategy candidates, parity detection and Z detection, are considered and compared. In addition, we study the effects of several realistic scenarios on the estimation protocol, including transmission loss, detection efficiency, dark counts, and those which are a combination thereof. Finally, we exhibit a proof-of-principle experiment, the results suggest a resolution enhancement effect with a factor of 3.72.

Orbital-angular-momentum-enhanced estimation of sub-Heisenberg-limited angular displacement with two-mode squeezed vacuum and parity detection.

We report on an orbital-angular-momentum-enhanced scheme for angular displacement estimation based on two-mode squeezed vacuum and parity detection. The sub-Heisenberg-limited sensitivity for angular displacement estimation is obtained in an ideal situation. Several realistic factors are also considered, including photon loss, dark counts, response-time delay, and thermal photon noise. Our results indicate that the effects of realistic factors on the sensitivity can be offset by raising orbital angular momentum quantum number ℓ. This implies that the robustness and the practicability of the system can be improved via raising ℓ without changing mean photon number N.

Super-sensitive angular displacement estimation via an SU(1,1)-SU(2) hybrid interferometer.

In this paper, we propose a protocol for the estimation of angular displacement based upon orbital angular momentum and an SU(1,1)-SU(2) hybrid interferometer. This interferometer consists of an optical parametric amplifier, a beam splitter, and reflection mirrors; the balanced homodyne detection is used as the detection strategy. The results indicate that super-resolution and super-sensitivity can be achieved with an ideal scenario. Additionally, we study the effect of photon loss on resolution and sensitivity, and the robustness of our protocol is also discussed. Finally, the advantage of our protocol compared with an SU(1,1) protocol is demonstrated, and the merits of orbital angular momentum-enhanced protocol are summarized.

Effects of imperfect elements on resolution and sensitivity of quantum metrology using two-mode squeezed vacuum state.

It has been demonstrated that using two-mode squeezed vacuum state for phase estimation can break the Heisenberg limit. Our results reveal that the two-mode squeezed vacuum state is also applied to the optical rotation angle measurement. In our scheme, the resolution and sensitivity of the optical rotation angle signal are the same as the case of phase estimation. For the parameter estimation, phase or rotation angle, we discuss the influences of several imperfect factors on the resolution and sensitivity. First, the effect that the upper limit of photon-number resolving has on the maximum amount of available quantum Fisher information has been analyzed. Then, we have also studied the impacts of both the transmission efficiency in the transmission process and the detection efficiency on the detection results. Finally, conditions where all of the above imperfect elements are taken into account at the same time have also been explored. Additionally, other imperfect factors such as squeezing efficiency and dark counts are briefly discussed.

Super-resolving angular rotation measurement using binary-outcome homodyne detection.

There has been much recent interest in high precision angular rotation measurement using photon orbital angular momentum to realize super-resolving angular rotation measurement. It is well known that quantum detection strategies can obtain a quantum-enhanced performance. Here, we prove that binary-outcome homodyne detection method can obtain a narrower signal peak, showing better resolution compared with the existing data processing method. Since the photon loss is unavoidable in the actual non-ideal optical system, this paper further discusses the impact of photon loss on the resolution and sensitivity of angular rotation measurement with binary-outcome homodyne detection method.

Ultra-sensitive and super-resolving angular rotation measurement based on photon orbital angular momentum using parity measurement.

Photon orbital angular momentum has led to many novel insights and applications in quantum measurement. Photon orbital angular momentum can increase the resolution and sensitivity of angular rotation measurement. However, quantum measurement strategy can further surpass this limit and improve the resolution of angular rotation measurement. This Letter proposes and demonstrates a parity measurement method in angular rotation measurement scheme for the first time. Parity measurement can make the resolution superior to the limit of the existing method. The sensitivity can be improved with higher orbital angular momentum photons. Moreover, this Letter gives a detailed discussion of the change of resolution and sensitivity in the presence of photon loss.