Application Cases

Experiment Name: Preparation of Long-Lifetime Magnon-Sensitive Spin Wave Optical-Atomic Entanglement Source

Test Equipment: High-voltage amplifier, Function generator, Power amplifier, Electro-optic modulator, Laser, Optical isolator, Phase delay box, Piezoelectric ceramic, etc.

Experimental Process:

Figure 1: PDH Frequency Locking Setup
Note: Laser: Laser, ISO: Optical isolator, EOM: Electro-optic modulator, Poweramp: Power amplifier, Oscillator: Function generator, DelayBox: Phase delay box, Mixer: Mixer, HP: High-pass filter, LP: Low-pass filter, PID: Proportional-integral controller, HV: High-voltage amplifier, Detector: Detector, PZT: Piezoelectric ceramic.

The fabricated mode cleaner was frequency-locked using the PDH technique, as shown in Figure 1. First, the laser frequency was locked to the atomic transition line using saturation absorption spectroscopy. A laser beam of a specific frequency, emitted from the laser, passed through an isolator (ISO), an electro-optic modulator (EOM), and a lens, and entered the three-mirror cavity through the center of mirror M2. The waist radius of the laser beam after passing through the lens matched the waist radius of the three-mirror cavity. A weak beam transmitted from the concave mirror M3 was detected by a detector, which converted the cavity mode information into an electrical signal. This signal passed through a high-pass filter and entered a mixer. The sinusoidal signal from the function generator (Oscillator) was split into two paths: one was amplified by a power amplifier (Poweramp) and applied to the electro-optic modulator (EOM) to phase-modulate the laser, while the other was phase-delayed by a phase delay box (DelayBox) and entered the mixer (Mixer). The mixed signal was filtered by a low-pass filter to remove high-frequency components, extracting the error signal. The weak error signal was optimized by a proportional-integral controller (PID). After optimizing the error signal by adjusting the phase delay box and PID parameters, it was amplified by a high-voltage amplifier and fed back to the piezoelectric ceramic (PZT). The PZT drove the cavity mirror M3 to vibrate at high frequency, thereby changing the cavity length to resonate the laser with the three-mirror cavity mode, achieving locking of the mode cleaner. The measured transmission efficiency of the mode cleaner was 55%. After passing through two filters, the incoherent light in the write/read beams could be filtered out, improving the signal-to-noise ratio of single-photon measurements.

Experimental Results:

Figure 2: Recovery Efficiency of Magnon-Sensitive Spin Wave vs. Storage Time

Figure 2 shows the relationship between the recovery efficiency of the magnon-sensitive spin wave and the storage time. In the experiment, the total detection efficiency of Stokes photons propagating to the single-photon detector was η = 22.8%. For each detection of N Stokes photons, the coincidence counts between single-photon detectors DS1 and DS2 with DAS1 and DAS2 were NAS, allowing the calculation of the recovery efficiency γ. To optimize the storage lifetime of the magnon-sensitive spin wave, the current in the geomagnetic field coil was adjusted to precisely compensate for the ambient magnetic field, using the oscillation of recovery efficiency with storage time as a reference. The relationship between recovery efficiency and storage time after precise compensation is shown in Figure 2. The recovery efficiency γ₀ at storage time t₀ = 0 μs was 15.8%, and γ₁ at storage time t₁ = 900 μs was 5.85%. The recovery efficiency tended to decrease as the storage time increased. The fitted function yielded a 1/e storage lifetime of t₀ = 900 μs.

Figure 3: Parameter S vs. Storage Time

To investigate the relationship between the entanglement of light and atoms and the storage time, we measured the Bell parameter S at different storage times. The Bell parameter S and the Clauser-Horne-Shimony-Holt (CHSH) inequality are commonly used to determine whether entangled photon pairs are generated. The red dots in Figure 3 represent the measured Bell parameter S values at different storage times t. At storage time t = 0 μs, the Bell parameter S = 2.58 ± 0.03 violated the Bell inequality by 19.3 standard deviations. At storage time t = 900 μs, the Bell parameter S = 2.10 ± 0.03 violated the Bell inequality by 3.3 standard deviations. The Bell parameter S decreased as the storage time t increased.

High-Voltage Amplifier Recommendation: ATA-7050

Figure: ATA-7050 High-Voltage Amplifier Specifications

The experimental materials in this article have been compiled and released by Xi'an Aigtek Electronics. For more experimental solutions, please continue to follow the Aigtek official website. Aigtek is a high-tech enterprise in China specializing in the research, development, production, and sales of measurement instruments. The company has consistently focused on the R&D and manufacturing of test instrument products such as high-voltage amplifiers, voltage amplifiers, power amplifier modules, and high-precision current sources.