Inside Quanfluence’s Balanced Detector: High-Bandwidth, Low-Noise Photonic Precision
Introduction
In the expanding world of quantum optics, the precision detection of light is paramount. One core tool in our arsenal is the balanced detector—an instrument designed to measure the difference in optical power between two input beams with extraordinary sensitivity. At Quanfluence, we’ve developed and refined a high-performance, balanced detector that is now being shipped to customers worldwide. This blog examines how it operates, what makes ours unique, and its place within the broader landscape of quantum and photonics research.
What is a Balanced Detector?
A balanced detector typically consists of two matched photodiodes and a differential transimpedance amplifier (TIA). When two beams, referred to as signal and reference, are incident on the photodiodes, the detector outputs a voltage proportional to the optical power difference between them. Common-mode signals (such as noise or DC offset) are rejected, enabling extremely sensitive detection of small signal variations. This is especially valuable in homodyne and heterodyne detection schemes used in quantum optics, telecommunications, and precision metrology.
Quanfluence's Approach
Our balanced detector is designed with quantum-grade performance and global usability in mind:
- • Wide Bandwidth: Supporting detection from low frequencies up to several hundred MHz, making it ideal for pulsed and continuous-wave systems.
- • Low Noise Floor: Carefully matched photodiodes, careful component selections and design and optimized PCB layout ensure high common-mode rejection and minimal dark noise.
- • Support for Free-Space and Fiber Inputs: Designed to integrate seamlessly into both free-space optical benches and fiber-coupled setups.
- • Wavelength Flexibility: Compatible with a wide range of wavelengths across the visible and near-infrared spectrum. We also offer custom designs to support higher quantum efficiency at specific wavelengths.
- • Compact and Robust Form Factor: Our detector is encased in a precision-machined enclosure, making it easy to integrate into both benchtop and field-deployed setups.
- • Global Shipping and Support: Quanfluence detectors are in use across North America, Europe, and Asia in labs and pilot production environments.
Applications
- • Quantum Optics: Essential for balanced homodyne detection (BHD) in continuous-variable quantum computing and quantum key distribution.
- • Optical Coherence Tomography: Enables differential measurement in biomedical imaging, especially ophthalmology.
- • Laser Noise Characterization: Ideal for detecting small intensity fluctuations in high-performance laser systems.
- • Signal Demodulation: Used in advanced communication setups to extract phase or amplitude information.
What Makes Ours Different?
Quanfluence’s detector isn’t just sensitive it’s engineered for reliability, low power operation, and ease of use. We’ve focused on:
- • Minimizing electronic noise and maximizing quantum efficiency
- • Tightly matched optical and electronic response
- • Mechanical stability across temperature ranges
- • Connector flexibility (SMA outut, FC/APC input, and free-space compatible mounts)
- • Custom tuning for wavelength-specific applications and enhanced quantum efficiency
Use Case: Balanced Homodyne Detection in CV Quantum Computing
In continuous-variable (CV) quantum photonic systems, qubit states are encoded in the quadrature amplitudes of the electromagnetic field. To read and manipulate these quantum states, balanced homodyne detection (BHD) is employed, which measures the interference between a weak quantum signal and a strong local oscillator.
Quanfluence’s balanced detector is at the centre of this measurement. With its low noise floor, high bandwidth, and precise optical matching, the detector enables reliable extraction of quadrature information. This is needed for implementing quantum gates, state tomography, and feedforward control. In our quantum computing architecture, the detector is used downstream of interferometric circuits, where the output is sent to both classical processing units and real-time control electronics. The ability to resolve small amplitude differences with high fidelity ensures that the measurement-induced collapse is accurate and that operations like Gaussian unitaries and displacement gates can be reliably performed.
This real-world integration of our balanced detector in homodyne setups highlights its importance, not just as a component, but as a cornerstone of quantum state manipulation.
Looking Ahead: Co-Packaged Systems for Next-Gen Detection
Quanfluence is advancing toward the co-packaging of our balanced photonic detector with a next-generation high-bandwidth transimpedance amplifier (TIA) designed in-house. These will be realized on two separate chips, a photonic chip for the detector and an electronic chip for the amplifier. These will be co-packaged, creating a compact, balanced detector.
This approach reduces parasitic losses, improves signal integrity, and enables shorter electrical paths between the photodiodes and TIA, supporting even higher bandwidths and lower noise. We are focusing on packaging simplicity and performance for scalable use in CV quantum systems. These enhancements are aimed at making the detector more compact, lower power, and better suited for integration into Quanfluence’s future quantum hardware stacks, as well as availability to 3rd party users.
To request detailed specs or a demo unit, reach out to us at info@quanfluence.com.