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arXiv:1809.04319 · Physical Review Applied

Excess Loss in Homodyne Detection Originating from Distributed Photocarrier Generation in Photodiodes

Takahiro Serikawa, Akira Furusawa

Published Dec 7, 2018• 10 citations
arXivHTMLPDF

Abstract

Optical homodyne (single-frequency) measurement is a key technology in optical quantum information processing and key distribution, since it can realize high-speed quantum measurement with a high signal-to-noise ratio. Researchers show that photodiodes have an intrinsic noise mechanism in the photodetection process, due to distributed photocarrier generation, and the excess noise cause an effective optical loss in homodyne detection at high frequencies. They evaluate this excess loss theoretically and experimentally, showing that it depends on the photodiode's material, and suggesting further requirements for high-efficiency, high-speed hardware.

DOI
10.1103/physrevapplied.10.064016

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Optical homodyne (single-frequency) measurement is a key technology in optical quantum information processing and key distribution, since it can realize high-speed quantum measurement with a high signal-to-noise ratio. Researchers show that photodiodes have an intrinsic noise mechanism in the photodetection process, due to distributed photocarrier generation, and the excess noise cause an effective optical loss in homodyne detection at high frequencies. They evaluate this excess loss theoretically and experimentally, showing that it depends on the photodiode's material, and suggesting further requirements for high-efficiency, high-speed hardware.
Discrete-modulated continuous-variable quantum key distribution with homodyne detection is widely recognized for its ease of implementation, efficiency with respect to error correction, and its compatibility with modern optical communication devices.However, recent studies report that the application of homodyne detection obtains poor tolerance to excess noise and insufficient transmission distance, hence seriously restricting the large-scale deployment of quantum secure communication networks.In this paper, we propose a homodyne detection protocol using the quadrature phase shift keying technique.By limiting information leakage, our proposed protocol enhances excess noise tolerance to a high level.Furthermore, we demonstrate that homodyne detection performs better than heterodyne detection in quaternary-modulated continuous-variable quantum key distribution under the untrusted detector noise scenario.The security is analyzed using the tight numerical method against collective attacks in the asymptotic regime.Our results imply that the current protocol can distribute keys in nearly intercity area and, thus, paves the way for constructing low-cost quantum secure communication networks.
We developed a high speed homodyne detector in the telecommunication wavelength region for a Gaussian-modulated coherent-state quantum key distribution experiment. We are able to achieve a 100 MHz bandwidth, ultra-low electronic noise and pulse-resolved homodyne detector. The bandwidth of this homodyne detector has reached the same order of magnitude of the best homodyne detectors reported. By overcoming photodiode response functions mismatch, choosing proper laser sources, ensuring the homodyne detector linearity and stabilizing the homodyne detection system, we demonstrate that the homodyne detector has a 10 dB shot-noise-to-electronic-noise ratio in the time domain at a local oscillator of 5.4*10^8 photons/pulse at a laser repetition rate of 10 MHz. With this homodyne detector, we expect to ncrease our GMCS QKD experiment speed by 100 times, which will improve the key generation rate by 1-2 orders of magnitude.
High-frequency squeezed states are important for quantum metrology and information processing, but quadrature measurements at gigahertz frequencies remain challenging. Balanced homodyne detection (BHD), the standard approach, requires closely matched complex transfer functions in both photodetection channels to suppress local-oscillator (LO) noise and maintain a well-defined readout quadrature. This matching becomes increasingly difficult at high bandwidths. Strongly asymmetric single-photodiode homodyne detection avoids this requirement, but achieving high signal efficiency and shot-noise clearance typically requires hundreds of milliwatts of LO power and does not suppress technical LO sidebands. I propose cavity-assisted homodyne detection, in which the quantum field and LO enter separate ports of an impedance-matched traveling-wave cavity. The resonant LO carrier is transmitted to the photodetector, where it beats with off-resonant signal sidebands reflected from the cavity. At the same time, technical LO sidebands outside the cavity linewidth are suppressed. I derive the quantum input-output relations and linearized photocurrent including intracavity loss, and show that near-unity signal-transfer efficiency can be achieved at moderate incident LO power. The cavity linewidth and free spectral range determine the usable detection band.
Low-noise, efficient, phase-sensitive time-domain optical detection is essential for foundational tests of quantum physics based on optical quantum states and the realization of numerous applications ranging from quantum key distribution to coherent classical telecommunications. Stability, bandwidth, efficiency, and signal-to-noise ratio are crucial performance parameters for effective detector operation. Here we present a high-bandwidth, low-noise, ultra-stable time-domain coherent measurement scheme based on balanced homodyne detection ideally suited to characterization of quantum and classical light fields in well-defined ultrashort optical pulse modes.
With quantum information processing in mind, homodyne optical amplification tremendously enhances the sensitivity of spin noise spectroscopy applied to delicate few- and single-spin systems. In realizing the allied experimental techniques, the authors are able to boost the low-frequency spin noise signal of a few remaining impurities in an isotopically enriched Rb vapor above the electronic noise level dictated by the photodetector system. This proof-of-principle experiment advances semiconductor spin research and facilitates higher-order spin noise measurements on semiconductor qubits, such as single (In,Ga)As quantum dots.
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