Low Noise Balanced Homodyne Detector for Quantum Noise Measurement

Abstract

The research of quantum noise in the interaction of laser and atoms plays a critical role in quantum optical experiments. The measurement of quantum noise is mainly based on the balanced homodyne detection method. Here, we reported a balanced homodyne detector with low noise, high gain, and high common-mode rejection ratio (CMRR) at the wavelength of 795 nm. By optimizing the selection of components and PCB layout, a minimum electronic noise of −96.7 dBm is obtained. Over the range of 1 MHz to 5 MHz, we get a flat CMRR above 59 dB and a linear gain regime, which can enable a shot noise measurement with the laser power of 100 μw. The developed detector can be used in quantum coherent experiments with a weak probe laser of power down to tens of microwatts.

Research on large-bandwidth balanced homodyne detector for quantum detection

“…We also focus on the need to tightly control the junction capacitance at the input. The introduction of tiny junction capacitance will cause the bandwidth of BHD to be reduced, so we need to control the pin length of the connected PD because it will also be connected to the circuit as a medium [14] . After perfecting the circuit structure of the BHD, we need to place the BHD circuit board in an insulated aluminum shielding box to reduce the interference of external noise on the BHD.…”

“…After passing through the beam splitter, connect one end to the adjustable optical attenuator and the other end to the fiber extension cable. In this way, the light source can be better adjusted when measuring the common mode suppression ratio, so that the amplitude of the light source at both ends of the input is the same and the phase difference is maintained at 180°, so as to better achieve the common mode suppression effect [14] . The spectrum of the two output signals is organized into a graph, as shown in Figure 4, it can be seen from the red spectrum in the Figure 4, the power output of a single photodiode at the 100MHz fundamental harmonic is about 77.5 dBm.…”