Application Cases

Experiment Title: Quantum Noise Locking Experiment

Testing Equipment: High Voltage Amplifier, Oscilloscope, Laser, Photodetector, Spectrum Analyzer, Bandpass Filter, Low Pass Filter, Piezoelectric Ceramic, etc.

Experiment Process:

Figure 1: Schematic Diagram of the Quantum Noise Feedback Stabilization Vacuum Squeezed Light Phase Device. A green light with a wavelength of 532nm is used to pump a dual-wavelength resonant OPO cavity to generate vacuum squeezed light with a wavelength of 1064nm. The noise of the squeezed light is measured using a balanced homodyne detection method. The clever vacuum squeezed light noise signal is locked to the balanced homodyne phase through a feedback loop composed of a spectrum analyzer and a lock-in amplifier. Laser: A fully solid-state single-frequency frequency-doubled Nd:YV04/KTP laser, with output wavelengths of 1064nm and 532nm, PD1/PD2: Photodetectors, SA: Spectrum Analyzer model, BPS: Bandpass Filter, ED: Envelope Detector, LPF: Low Pass Filter, HV: High Voltage Amplifier, PZT: Piezoelectric Ceramic.

The experimental process of quantum noise locking squeezed light phase in balanced homodyne detection is shown in Figure 1. The upper part is the optical path, and the lower part is the electrical circuit. First, squeezed light needs to be prepared. The fully solid-state single-frequency frequency-doubled Nd:YV04/KTP laser outputs infrared light at 1064nm and green light at 532nm, which are used as the local oscillator light for balanced homodyne detection and the pump light for the OPO cavity, respectively, to prepare vacuum squeezed light. The noise curve of the squeezed light measured by the spectrum analyzer is shown as curve (a) in Figure 2, and curve (b) is the shot noise limit. The parameters of the spectrum analyzer are set to a frequency of 2MHz, Span at zero, detection resolution bandwidth at 300kHz, display bandwidth at 30kHz, and sweep time at 533.6ms. It can be seen from the figure that the light field has achieved about 2dB of squeezing and 4.5dB of anti-squeezing at a frequency of 2MHz.

Figure 2: Spectrum Analyzer Noise Curve of Squeezed Light at 2MHz. (a) Line represents squeezed light noise, (b) line represents shot noise limit. Vacuum squeezed light with a squeezing degree of 2dB is obtained at 2MHz.

Experimental Results:

Figure 3: Error signal monitored by the oscilloscope and noise signal demodulated and output by the spectrum analyzer. The thicker blue curve represents the noise signal, and the smoother yellow curve represents the error signal. The error signal corresponds to the maximum or minimum value of the noise line at zero, which corresponds to the anti-squeezed state and squeezed state of the light field, respectively. This is in good agreement with the theoretical values.

The intensity noise signal of the squeezed light measured by the spectrum analyzer is demodulated and filtered within the spectrum analyzer and then input into the lock-in amplifier, as shown in the SA part of Figure 1. The thicker blue curve in Figure 3 is the spectrum analyzer output signal monitored by the oscilloscope. The lock-in amplifier outputs a modulation signal with a frequency of 30kHz, which is loaded onto the piezoelectric ceramic on the mirror in the local oscillator light path, equivalent to adding a phase modulation signal to the local oscillator light. This piezoelectric ceramic mounted on the mirror is also used in the feedback loop of quantum noise locking. The smoother yellow curve in Figure 3 is the error signal monitored by the oscilloscope, which can be optimized by adjusting the parameters of the lock-in amplifier. Finally, the error is input into the high voltage amplifier and then fed back to the PZT mounted on the mirror holder to lock the phase of the squeezed light. The noise curves of the squeezed light at a frequency of 2MHz measured by the spectrum analyzer after phase locking are shown in Figures 5A and 5B. It is observed experimentally that the stability of locking the squeezed light phase using quantum noise locking is higher than that of locking the anti-squeezed state.

Figure 4: Noise Curve of Squeezed Light Phase Locked at Low Frequencies Measured by Low Frequency Spectrum Analyzer. Curve (a) is the shot noise limit, and curve (b) is the locked squeezed noise curve. After locking the phase of the squeezed light in balanced homodyne detection using the quantum noise method, the noise of the squeezed light at low frequencies is measured by a low-frequency spectrum analyzer. The measured low-frequency squeezed light noise is shown in Figure 4. Curve (a) in the figure is the shot noise limit, and curve (b) is the locked squeezed noise curve. It can be seen that after locking the phase of the squeezed light in balanced homodyne detection using the quantum noise method, squeezing can be observed in frequency bands above 3kHz.

Figure 5: Spectrum Analyzer Quantum Noise Locking Vacuum Squeezed Light Effect Diagram. Curves (a) and (b) in A and B are the squeezed light noise and shot noise limit, respectively, and curve (c) represents the locked phase squeezed and anti-squeezed noise. Experimentally, the stability of locking the squeezed state phase is higher than that of locking the anti-squeezed state.

High Voltage Amplifier Recommendation: ATA-4315

Figure: Specifications of the ATA-4315 High Voltage Power Amplifier

This material is compiled and released by Aigtek Antai Electronics. For more case studies and product details, please continue to follow us. Xi'an Aigtek Antai Electronics has become a widely recognized supplier of instruments and equipment with a broad product line and considerable scale in the industry. Sample machines are available for free trial.