Homodyne Research Articles

Homodyne detection efficiency analysis of coherent lidar based on a hybrid algorithm

Atmospheric turbulence-induced phase variations affect the homodyne detection efficiency of the coherent lidar, which further affects the performance of the lidar. Adaptive optics (AO) is an effective method to correct turbulence-induced wavefront aberrations. In this paper, a coherent lidar wavefront correction technique based on a hybrid algorithm of stochastic parallel gradient descent (SPGD) and simulated annealing (SA) is proposed on the basis of a theoretical analysis. The simulation results verify that the hybrid algorithm can significantly improve the efficiency of homodyne detection in coherent lidar. The results show that the hybrid algorithm has the characteristics of fast convergence speed and strong correction ability. The conclusion of this paper provides a reference for the design of the coherent lidar AO system.

Sub-1 V/cm E-FISH-based picosecond electric field measurements in atmospheric pressure air

Abstract We report on the development of a highly sensitive Electric Field Induced Second Harmonic (E-FISH) generation diagnostic setup capable of measuring electric field strengths as low as 1 V/cm at the picosecond time scale under atmospheric pressure conditions. This unprecedented sensitivity is achieved through passive homodyne detection, which utilizes stray signals generated by an optical component in the beam path. Our detection limit of 0.3–0.5 V/cm represents an improvement of over 2–3 orders of magnitude compared to previous reports (100 – 1000 V/cm) in the literature. Additionally, we demonstrate sensitivity to the polarity of the electric field. Experimental results are corroborated by simulations of the 400 ps time-resolved homodyne process, offering deeper insights into the enhanced detection capabilities and the system’s ability to resolve the field sign.

Scaling and networking a modular photonic quantum computer.

Photonics offers a promising platform for quantum computing1-4, owing to the availability of chip integration for mass-manufacturable modules, fibre optics for networking and room-temperature operation of most components. However, experimental demonstrations are needed of complete integrated systems comprising all basic functionalities for universal and fault-tolerant operation5. Here we construct a (sub-performant) scale model of a quantum computer using 35 photonic chips to demonstrate its functionality and feasibility. This combines all the primitive components as discrete, scalable rack-deployed modules networked over fibre-optic interconnects, including 84 squeezers6 and 36 photon-number-resolving detectors furnishing 12 physical qubit modes at each clock cycle. We use this machine, which we name Aurora, to synthesize a cluster state7 entangled across separate chips with 86.4 billion modes, and demonstrate its capability of implementing the foliated distance-2 repetition code with real-time decoding. The key building blocks needed for universality and fault tolerance are demonstrated: heralded synthesis of single-temporal-mode non-Gaussian resource states, real-time multiplexing actuated on photon-number-resolving detection, spatiotemporal cluster-state formation with fibre buffers, and adaptive measurements implemented using chip-integrated homodyne detectors with real-time single-clock-cycle feedforward. We also present a detailed analysis of our architecture's tolerances for optical loss, which is the dominant and most challenging hurdle to crossing the fault-tolerant threshold. This work lays out the path to cross the fault-tolerant threshold and scale photonic quantum computers to the point of addressing useful applications.

Dual balanced readout for scattered light noise mitigation in Michelson interferometers

Ground-based gravitational wave detectors use laser interferometry to detect the minuscule distance change between test masses caused by gravitational waves. Stray light that scatters back into the interferometer causes transient signals that can cover the same frequency range as a potential gravitational wave signal. This scattered light noise is a potentially limiting factor in current and future detectors thus making it relevant to find new ways to mitigate it. Here, we demonstrate experimentally a technique for the subtraction of scattered light noise from the displacement readout of a Michelson interferometer. It is based on using a balanced homodyne detector at both the symmetric and the antisymmetric port. While we have been able to demonstrate a noise reduction of 13.2 dB, the readout scheme seems to be only limited by the associated noise couplings, i.e., shot noise and the coupling of laser noise. We also discuss challenges for using the dual balanced homodyne detection scheme in more complex interferometer topologies, which could lead to improvements in scattered light noise mitigation of gravitational wave detectors. Published by the American Physical Society 2025

Nonlinear and nonlinear-linear hybrid interferometers using coherent and squeezed vacuum states.

Classical and quantum states working in concert play an essential role in high-precision interferometry. In this regard, coherent combined with squeezed vacuum states are the most promising candidate. Here we complement this subject by comparing nonlinear and nonlinear-linear hybrid interferometers with homodyne detection as a readout strategy. For a high-photon coherent state, either of the two interferometers can provide the phase sensitivity approaching the quantum Cramer-Rao bound. Additionally, we discuss the impacts of photon loss during the transmission and readout stages. We find that a nonlinear interferometer is advantageous over a nonlinear-linear hybrid interferometer. With increasing photon number of the coherent state, the maximal tolerable lossy rate ensuring phase sensitivity beyond the shot-noise limit is close to 50%. Our work may deepen the understanding of quantum-enhanced interferometry using nonlinear dynamics.

Spontaneous photon emission by shaped quantum electron wavepackets and the QED origin of bunched electron beam superradiance

It has been shown that the spontaneous emission rate of photons by free electrons, unlike stimulated emission, is independent of the shape or modulation of the quantum electron wavefunction (QEW). Nevertheless, here we show that the quantum state of the emitted photons is non-classical and does depend on the QEW shape. This non-classicality originates from the shape dependent off-diagonal terms of the photon density matrix. This is manifested in the Wigner distribution function and would be observable experimentally through homodyne detection techniques as a squeezing effect. Considering a scheme of electrons interaction with a single microcavity mode, we present a QED formulation of spontaneous emission by multiple modulated QEWs through a build-up process. Our findings indicate that in the case of a density modulated QEWs beam, the phase of the off-diagonal terms of the photon state emitted by the modulated QEWs is the harbinger of bunched beam superradiance, where the spontaneous emission is proportional toNe2. This observation offers a potential for enhancement of other quantum electron interactions with quantum systems by a modulated QEWs beam carrying coherence and quantum properties of the modulation.

Effect of group-velocity dispersion on the generation of multimode pulsed squeezed light in a synchronously pumped optical parametric oscillator

Abstract Parametric down-conversion in a nonlinear crystal is a widely employed technique for generating quadrature squeezed light with multiple modes, which finds applications in quantum metrology, quantum information and communication. Here we study the generation of temporally multimode pulsed squeezed light in a synchronously pumped optical parametric oscillator (SPOPO) operating below the oscillation threshold, while considering the presence of non-compensated intracavity group-velocity dispersion. Based on the developed timedomain model of the system, we show that the dispersion results in mode-dependent detuning of the broadband supermodes of the pulsed parametric process from the cavity resonance due to temporal Gouy phase, as well as linear coupling between these supermodes. With perturbation theory up to the second order in the coupling coefficients between modes, we obtained a solution for the amplitudes of multiple supermodes given an arbitrary sub-threshold pump level. The dispersion affects the quantum state of the supermodes by influencing their squeezing level and the rotation of the squeezing ellipse. It also affects the entanglement among the supermodes, leading to reduced suppression of shot noise level as measured in the balanced homodyne detection scheme. Furthermore, our study highlights the potential of SPOPO with group-velocity dispersion as a testbench for experimental investigations of multimode effects in linearly evanescent coupled parametric oscillators.

The finite-size effect on continuous-variable quantum key distribution in the Terahertz band

We conducted a study to evaluate the performance of Terahertz Continuous Variable Quantum Key Distribution (THz CVQKD) systems in atmospheric conditions with the finite-size effect. Our research delved into the secure key rates and transmission distances of THz CVQKD for four protocols, all based on Gaussian coherent states, under the threat of collective Gaussian attacks. These protocols include reverse reconciliation with homodyne detection, direct reconciliation with homodyne detection, reverse reconciliation with heterodyne detection, and direct reconciliation with heterodyne detection. Our findings revealed distinctive key rates across various THz frequencies and protocols. However, the finite-size effect had a diminishing impact on the key rates of CVQKD in all scenarios. Fortunately, by harnessing a substantial number of keys exceeding 1012 and optimizing modulation variance, both the key rates and transmission distances of THz CVQKD can be significantly extended. This research contributes to advancing the practicality of THz CVQKD technology.

Experimental investigation of heralded Gaussification of phase-randomized coherent states of light

Probabilistic heralded Gaussification of quantum states of light is an important ingredient of protocols for distillation of continuous variable entanglement and squeezing. An elementary step of the heralded Gaussification protocol consists of interference of two copies of the state at a balanced beam splitter, followed by conditioning on the outcome of a suitable Gaussian quantum measurement on one output mode. When iterated, the protocol either converges to a Gaussian state or diverges. Here, we report on experimental investigation of the convergence properties of iterative heralded Gaussification. We experimentally implement two iterations of the protocol, which requires simultaneous processing of four copies of the input state. We utilize the phase-randomized coherent states as the input states, which greatly facilitates the experiment because these states can be generated deterministically, and their mean photon number can easily be tuned. We comprehensively characterize the input and partially Gaussified states by balanced homodyne detection and quantum state tomography. Our experimental results are in good agreement with theoretical predictions and they provide new insights into the convergence properties of heralded quantum Gaussification.

Advantage of Non‐Gaussian Operations in Phase Estimation via Mach–Zehnder Interferometer

AbstractThis study investigates the benefits of probabilistic non‐Gaussian operations in phase estimation using difference‐intensity and parity detection‐based Mach–Zehnder interferometers (MZI). An experimentally implementable model is considered to perform three different non‐Gaussian operations, namely photon subtraction (PS), photon addition (PA), and photon catalysis (PC) on a single‐mode squeezed vacuum (SSV) state. The findings reveal that all non‐Gaussian operations except one PC operation provide an advantage in either of the measurement schemes. This result is further supported by the analysis of the quantum Cramér–Rao bound. When accounting for the success probability of non‐Gaussian operations, two‐PC and four‐PA emerges as the most optimal operations in difference‐intensity and parity detection‐based MZI, respectively. Additionally, the corresponding squeezing and transmissivity parameters that yields the best performance are identified, making the study relevant for experimentalists. Furthermore, a general expression for the moment‐generating function is derived, which is useful in exploring other detection schemes such as homodyne detection and quadratic homodyne detection.

Dipole Moment of a Superatom.

Homodyne detection is used to measure the (collective) atomic dipole moment for an atomic ensemble that is prepared in a superposition of spatially phased Dicke states having at most two excitations (a so-called "superatom"). Homodyne detection allows one to isolate the contributions to the radiated intensity that depend linearly on the average value of the collective atomic dipole moment operator. Depending on whether the atom-reference field interference is constructive or destructive, either super-Poisson or sub-Poisson statistics for the combined field is observed.

Generation of two mode mechanical squeezing induced by nondegenerate parametric amplification

Squeezing light in an optomechanical system involves reducing quantum noise in one of the light’s quadratures through the interaction between optical and mechanical modes. However, achieving successful implementation requires careful control of experimental parameters, which can be challenging. Here, we investigate a two-mode squeezed light transfer from optical to mechanical modes induced by a non-degenerate optical parametric amplifier (OPA). The optomechanical system is driven by frequencies nearly resonant with the anti-stokes fields that can realize cooling mechanical oscillators and quantum state transfer within a resolved sideband (good cavity) limit. Our results show that when a non-degenerate OPA is placed inside the optical cavity, the degree of squeezing in both optical and mechanical modes is significantly enhanced. This leads to the two-mode squeezed light being transferred into two-mode mechanical squeezing in the presence of the non-degenerate OPA under weak optomechanical coupling strength. Interestingly, we found that with negligible thermal bath noise, the two-mode squeezed light completely transferred to yield 50% mirror-mirror squeezing. In contrast, at higher thermal noise, the transfer of squeezed light is weak, causing the system to lose its quantum properties and behave more classically. Furthermore, we have shown that the degree of squeezing in the weak coupling regime drastically decreases with increasing mechanical dissipation rates. We believe that our scheme can achieve strong mechanical squeezing in hybrid optomechanical systems and facilitate homodyne detection to measure the quadratures of the squeezed light.

Broadband generation and tomography of non-Gaussian states for ultra-fast optical quantum processors

Quantum information processors benefit from high clock frequencies to fully harness quantum advantages before they are lost to decoherence. All-optical systems offer unique benefits due to their inherent 100-THz carrier frequency, enabling the development of THz-clock frequency processors. However, the bandwidth of quantum light sources and measurement devices has been limited to the MHz range, with nonclassical state generation rates in the kHz range. In this study, we demonstrated broadband generation and quantum tomography of non-Gaussian states using an optical parametric amplifier (OPA) as a squeezed light source and an optical phase-sensitive amplifier (PSA). Our system includes a 6-THz squeezed-light source, a 6-THz PSA, and a 66-GHz homodyne detector. We successfully generated non-Gaussian states at a 0.9 MHz rate with sub-nanosecond wave packets using a continuous-wave laser. The performance is currently limited by the jitter of superconducting detectors, restricting the usable bandwidth to 1 GHz. Our technique extends the bandwidth to GHz, potentially increasing non-Gaussian state generation rates for practical optical quantum processors using OPAs.

Frequency tuning of a squeezed vacuum state using interferometric enhanced acousto-optic effect.

Quantum frequency conversion is one of the important tools for quantum information processing. So far, the frequency conversion of continuous variable quantum state in radio frequency range has not been demonstrated yet. Here, we experimentally demonstrate the optical frequency fine tuning of a squeezed vacuum state by using an acousto-optic modulator based bi-frequency interferometer. The systematic efficiency of the frequency tuning device is 91%, which is only confined by the optical transmission efficiency of the acousto-optic modulators. The amount of frequency tuning is 80 MHz, which is orders of magnitude larger than the line-width of the laser used to generate the squeezed state and can, in principle, be further extended. A squeezed vacuum state with -3.47 ± 0.02 dB squeezing level is sent to the frequency tuning device, and a squeezing level of -1.98 ± 0.02 dB is directly measured by a fiber coupled homodyne detector after the frequency tuning. Our scheme can also be applied to a variety of other quantum optical states as well and will serve as a handy tool for quantum networks.

Retraction Note: Homodyne detection based multiple-beam WDM FSO communication system under various environmental conditions

Retraction Note: Homodyne detection based multiple-beam WDM FSO communication system under various environmental conditions

Implementation of Optical Coherent Communication System between Two Computers

This work represents implementation and investigation of optical coherent communication system between two computers. A single mode optical fiber is selected as transmission medium. The data are sent via the RS-232 standard interface with a bit rate of 9.6 kbps from personal computer (PC1) by line receive to convert the data from electrical levels (-12/+12 V) into TTL level (0/5 V). The modulation of this data was accomplished by internal modulation using laser diode type (HFCT-5208M) 1310 nm wavelength. The optical D-coupler was used to combine the optical signal that come from laser source with optical signal of laser local oscillator (OTS-304XI) at 1310/1550 nm wavelength to obtain coherent (homodyne and heterodyne) detection respectively. A PIN photodetector (HFCT-5208M) is used. Calculations of Signal to Noise Ratio (SNR) and Bit Error Rate (BER) for coherent detection were measured at different length of the optical fiber. Result show that high SNR and low BER for heterodyne detection than for homodyne detection.

Practical approach to extending baselines of telescopes using continuous-variable quantum information

Abstract Interferometric telescopes are instrumental for the imaging of distant astronomical bodies, but optical loss heavily restricts how far telescopes in an array can be placed from one another, leading to a bottleneck in the resolution that can be achieved. An entanglement-assisted approach to this problem has been proposed by (Gottesman et al 2011 Phys. Rev. Lett. 109 070503), as a possible solution to the issue of optical loss if the entangled state can be distributed across long distances by employing a quantum repeater network. In this paper, we propose an alternative entanglement-assisted scheme that interferes a two-mode squeezed vacuum state with the astronomical state and then measures the resulting state by means of homodyne detection. We use a continuous-variable approach and compute the Fisher information with respect to the mutual coherence of the astronomical source. We show that when the Fisher information is observed cumulatively at the rate at which successful measurements can be performed, our proposed scheme does not outperform the traditional direct detection approach or the entanglement-assisted approach of GJC12.

Enhancement of single-photon level signal detection based on phase sensitive amplification strategy

Abstract We investigate the ability of phase-sensitive amplification (PSA) to noiselessly amplify the preferred quadrature components of single-photonsignals that are limited by phase fluctuations relative to the pump. We presenta PSA enhancement strategy that is more realistic for possible experimentalrealization and is expected to significantly improve the detection of weaksignals at the single-photon level and obtain more useful information. Our studyshows that with a large PSA gain, proper transmissivity allows both direct and
balanced homodyne detections to operate optimally simultaneously, and effectively improves the noise figure degradation owing to the internal losses and non-ideal detection efficiency.

All-fiber IPDA lidar for CH4 leakage monitoring using InGaAs/InP single-photon detector.

An integrated path differential absorption (IPDA) lidar for CH4 leakage monitoring is proposed and demonstrated. In the simplified all-fiber optical layout, a homemade InGaAs/InP single-photon detector (SPD) using multi-channel technique with multi-mode fiber coupling is used to increase the maximum count rate and coupling efficiency. The system is calibrated in intensity and frequency domains. Firstly, the fluctuation of the laser power is compensated. Secondly, the dead time, afterpulsing probability and dark counts of the SPD are corrected. A mean relative difference of 0.84% between SPD and PIN photodetector is achieved. Thirdly, non-linear frequency scanning of the laser is measured by homodyne detection and analyzed in joint time-frequency domain. In the symmetry-calibration process, the absorbance spectra of up and down scanning are compared. Maximum difference less than 1% with mean difference of 0.33% is achieved within a span of 4 GHz around the center of absorbance spectrum. Finally, a demonstration experiment over ten days is carried out to analyze the accuracy and stability of the system. A mean deviation of 0.03% with standard deviation of 0.46% is verified at a distance of 12 m and a time resolution of 1 s. By attenuating the laser power from 2 mW to 0.02 mW, the performance of the system is degraded to a mean deviation of 1.32% with standard deviation of 4.33%.

Improving phase sensitivity of a hybrid interferometer with the two-mode squeezed coherent state

We investigate the enhancement of phase sensitivity of a nonlinear-linear hybrid interferometer with the input of the two-mode squeezed coherent state (TMSCS). With the TMSCS produced by four-wave mixing, the quantum Cramér-Rao bounds (QCRB) can beat the Heisenberg limit (HL). Under the phase matched conditions, the optimal phase sensitivity with the balanced homodyne detection measurement can beat the HL and approach QCRB. The effects of internal and external losses on the measurement accuracy are also discussed. The results demonstrate that the scheme is robustness against to internal losses and this protocol can resist external detection loss which is up to 39%. Our results improve the performance of hybrid interferometers and this scheme can find important practical applications in quantum metrology.