[Paper Review] Quantum LiDAR with Frequency Modulated Continuous Wave

Ming‐Da Huang, Zhan-Feng Jiang+6 more|arXiv (Cornell University)|Jul 21, 2023

Advanced Optical Sensing TechnologiesPhysics and Astronomy3 citations

TL;DR

This paper proposes a quantum-enhanced Frequency Modulated Continuous Wave (FMCW) LiDAR system using entangled frequency-modulated photons in a Mach-Zehnder interferometer. By leveraging quantum entanglement, it achieves $√{n}$ improvement in range precision and $n$-fold resolution enhancement in velocity measurement over classical FMCW LiDAR, without requiring quantum pulsed compression or additional nonlinear processes beyond entangled photon generation.

ABSTRACT

The range and speed of a moving object can be ascertained using the sensing technique known as light detection and ranging (LiDAR). It has recently been suggested that quantum LiDAR, which uses entangled states of light, can enhance the capabilities of LiDAR. Entangled pulsed light is used in prior quantum LiDAR approaches to assess both range and velocity at the same time using the pulses' time of flight and Doppler shift. The entangled pulsed light generation and detection, which are crucial for pulsed quantum LiDAR, are often inefficient. Here, we study a quantum LiDAR that operates on a frequency-modulated continuous wave (FMCW), as opposed to pulses. We first outline the design of the quantum FMCW LiDAR using entangled frequency-modulated photons in a Mach-Zehnder interferometer, and we demonstrate how it can increase accuracy and resolution for range and velocity measurements by $\sqrt{n}$ and $n$, respectively, with $n$ entangled photons. We also demonstrate that quantum FMCW LiDAR may perform simultaneous measurements of the range and velocity without the need for quantum pulsed compression, which is necessary in pulsed quantum LiDAR. Since the generation of entangled photons is the only inefficient nonlinear optical process needed, the quantum FMCW LiDAR is better suited for practical implementations. Additionally, most measurements in the quantum FMCW LiDAR can be carried out electronically by down-converting optical signal to microwave region.

Motivation & Objective

• To develop a practical quantum LiDAR system that overcomes the inefficiencies of existing pulsed quantum LiDAR architectures.
• To enable simultaneous, high-resolution range and velocity measurements using continuous-wave frequency modulation and quantum entanglement.
• To reduce reliance on inefficient nonlinear optical processes beyond entangled photon generation, enhancing system feasibility for on-chip integration.
• To demonstrate that microwave down-conversion of beat signals enables precise electronic measurement, improving signal processing robustness.

Proposed method

• The system employs a Mach-Zehnder interferometer with entangled frequency-modulated photons to coherently mix reference and echo signals.
• Triangular frequency modulation is used to generate a beat signal whose spectral components encode target range and velocity.
• Quantum Fisher information and Cramér-Rao bounds are derived to quantify the theoretical precision limits of the system.
• The resolution of range and velocity is determined by the discrete Fourier transform (DFT) of the quantum beating signal, which corresponds to maximum-likelihood estimators.
• The scheme leverages entanglement in both time and path degrees of freedom to enhance sensitivity and resolution.
• Signal processing is performed in the microwave domain via down-conversion, enabling high-precision electronic measurement of Doppler shifts.

Experimental results

Research questions

• RQ1 Can quantum FMCW LiDAR achieve simultaneous, high-resolution range and velocity estimation without quantum pulsed compression?
• RQ2 How does entanglement in frequency-modulated photons improve the precision and resolution of FMCW LiDAR compared to classical counterparts?
• RQ3 To what extent does the system's performance scale with the number of entangled photons $n$?
• RQ4 Can the system be practically implemented using integrated photonic platforms with minimal nonlinear optical losses?

Key findings

• The quantum FMCW LiDAR achieves a $√{n}$ improvement in range precision and $n$-fold enhancement in velocity resolution compared to classical FMCW LiDAR.
• With $n=2$ entangled photons, the resolution of range and velocity is improved by a factor of 2 compared to single-photon states.
• The system enables simultaneous measurement of range and velocity without requiring quantum pulsed compression, a key limitation in pulsed quantum LiDAR.
• The only inefficient nonlinear process is the generation of entangled photons, significantly reducing system complexity and loss compared to pulsed quantum LiDAR.
• Microwave down-conversion of the beat signal allows for high-precision electronic measurement, enhancing system stability and integration potential.
• The architecture is highly suitable for on-chip integration on platforms such as thin-film lithium niobate, enabling compact, energy-efficient quantum LiDAR systems.