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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Die-Level Balanced Homodyne Receiver for Squeezed Light Detection in the GHz Regime

Emmily Zaiser, Alessandro Trenti, Dinka Milovančev, Christoph Gasser, Horst Zimmermann, Hannes Hübel

Published Jun 23, 2025• 0 citations
Publisher

Abstract

Quantum receiver scalability and cost-effectiveness are crucial in the evolving quantum landscape. Application based on squeezed light (e.g. high-precision measurements and quantum communication), can profit especially from integrated and low-noise detectors. The presented die-level receiver is shown in figure 1 a) and combines a novel custom transimpedance amplifier (TIA) with commercial photodiodes (PDs) [1]. This offers a more scalable solution than bulk balanced homodyne detectors (BHDs) while being low-cost compared to fully customized receivers. This design targets a high bandwidth operation while maintaining low-noise properties for the detection of weak quantum signals. To characterize this receiver, we evaluate its performance through measurements of clearance, and common-mode rejection ratio (CMRR). Based on these parameters, a simulation for its performance in the squeezed light detection measurement is presented.

DOI
10.1109/cleo/europe-eqec65582.2025.11111128

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Quantum receiver scalability and cost-effectiveness are crucial in the evolving quantum landscape. Application based on squeezed light (e.g. high-precision measurements and quantum communication), can profit especially from integrated and low-noise detectors. The presented die-level receiver is shown in figure 1 a) and combines a novel custom transimpedance amplifier (TIA) with commercial photodiodes (PDs) [1]. This offers a more scalable solution than bulk balanced homodyne detectors (BHDs) while being low-cost compared to fully customized receivers. This design targets a high bandwidth operation while maintaining low-noise properties for the detection of weak quantum signals. To characterize this receiver, we evaluate its performance through measurements of clearance, and common-mode rejection ratio (CMRR). Based on these parameters, a simulation for its performance in the squeezed light detection measurement is presented.
The rapid development of continuous-variable quantum communication has driven an increasing demand for high-performance quantum signal processing modules. Among these, the balanced homodyne detector (BHD) has emerged as a leading solution for practical quantum state measurement due to its capability to provide complete quantum mechanical characterization. However, its performance is often constrained by limited bandwidth and high noise levels, primarily due to the reliance on bulk optical components and discrete receiver electronics. The dominant noise source in these systems typically stems from electronic noise, while imbalances in the optical path further degrade the signal-to-noise ratio (SNR) of the BHD. In this work, we present an adjustable integrated optical path to enhance the balance within the BHD system, along with a low-noise transimpedance amplifier (TIA) by employing optoelectronic co-design. Our design achieves a bandwidth of 2.5 GHz, an input-referred noise current of only 2 pA/√Hz in 180 nm CMOS technology, and a measured quantum shot noise clearance of 15 dB generated from a 700 μA photocurrent. This is the maximum quantum shot noise clearance at the same BHD photocurrent reported to date above the GHz bandwidth.
Squeezing-based quantum metrology has been extensively applied in the field of precision measurement. Performance characteristics of squeezed light are obtained by a balanced homodyne detector. Here, we report a large dynamic range balanced homodyne detector with low-noise and high-signal-to-noise-ratio (SNR) for broadband squeezed light measurement. We perform a comprehensive theoretical analysis of the SNR in a wide bandwidth and experimentally analyze the important printed circuit board (PCB) layout and electronic components. Consequently, in the 100 MHz frequency band, the SNR and common mode rejection ratio (CMRR) rise over 12.6 dB and 55 dB, respectively, and the electronic noise is suppressed below -90 dB. The directly observed squeezing level at 1550 nm with the specified detector is 11.8 dB at 2 MHz and 3.1 dB at 100 MHz.
A low-noise, high-speed balanced homodyne detector is demonstrated, combining a capacitive-feedback transimpedance amplifier implemented in 28 nm CMOS with a custom photonic integrated circuit fabricated in imec's iSiPP200 silicon photonics platform. The receiver achieves a 3-dB bandwidth of 7.6 GHz, a maximum shot noise clearance of 27 dB, a shot noise-limited bandwidth of 13.7 GHz and a common-mode rejection ratio up to 54.8 dB. These results demonstrate the suitability of CMOS capacitive-feedback transimpedance amplifiers for demanding quantum and coherent sensing optical applications, including continuous-variable quantum key distribution, quantum random number generation, and optical coherence tomography.
We present a design of balanced homodyne receivers suitable for ultra-low noise quantum applications such as continuous-variable quantum key distribution and quantum random number generation. For best noise and bandwidth performance a die-level low-parasitic photodiode together with a low-noise high-speed transimpedance amplifier are explored together with a planar lightwave circuit splitter chip serving as a photomixer. Bandwidths of 750 MHz and 2.6 GHz were accomplished while maintaining optimum noise performance, as evidenced by very high quantum-to-classical noise ratios of 26.8 and 18.6 dB, respectively. A common-mode rejection ratio of at least 40 dB was achieved for a frequency range of up to 1 GHz. Its application for continuous-variable quantum key distribution was evaluated by means of estimations under a strict untrusted receiver assumption, showing its potential for generating up to 43 Mbit/s secure-key rate over a reach of 10 km, whereas up to 100 Mbit/s could be supported at shorter reaches. Moreover, the high quantum-to-classical clearance values can enable high quality quantum random number generation at Gb/s rates. The multi-purpose operation of the designed balanced receivers for classical communications was examined showing reception sensitivities of −55.8 and −52.6 dBm at 500 Mbit/s and 1 Gbit/s quadrature phase shift keying transmission, respectively, using the 750 MHz receiver. The faster 2.6 GHz receiver enabled 10 Gbit/s duobinary transmission at −14.8 dBm sensitivity.
Performance of linear avalanche photodiode-based balanced homodyne receiver (APD BHD) is examined and compared to reference BHD based on PIN photodiodes, in terms of common mode rejection ratio (CMRR), quantum-to-classical noise clearance (QCNR) and sensitivity in coherent reception of quadrature phase shift keying (QPSK) modulation format. NIST randomness validation was performed on sampled data for quantum random number generator (QRNG). Achieved CMRR values were 50 dB and 30 dB at 100 MHz and 1 GHz, respectively. QCNR of 20 dB at low input power of −20 dBm was demonstrated. Optical sensitivity of APD BHD coherent receiver compared to its PIN BHD counterpart can be improved by 3 dB at low local oscillator (LO) powers, whereas for high LO powers the sensitivity of APD BHD approaches the values for PIN BHD.
Squeezed light is a non-classical state of light in which the uncertainty in the electricfield strength at certain phases of oscillation is reduced below the vacuum noise level,at the cost of increased uncertainty at other phases. It has applications ranging fromgravitational wave detection to quantum communication, where the bandwidth of thesqueezed states directly limits protocol speed. Squeezed light is commonly measured us-ing balanced homodyne detection, in which the attainable squeezing level is restrictedby the photodetector’s quantum efficiency and dark noise. Currently, no commerciallyavailable photodetector combines high quantum efficiency with low dark noise over alarge bandwidth. This thesis presents the design and construction of a photodetectorintended to address this gap, with the aim of achieving high quantum efficiency and suf-ficient dark noise clearance over at least 1 GHz of bandwidth. The design was guidedby LTspice simulations and implemented on a two-layer printed circuit board. Twocommercially available reference detectors were characterised, illustrating the trade-offbetween high quantum efficiency and large bandwidth. Since the photodiodes for thenew detector had not arrived at the time of completion, its characterisation remains tobe carried out.