Continuously tunable modulation scheme for homodyne detection and state tomography.

Area of Science:

• Quantum Optics
• Quantum Information Science

Background:

• Homodyne detection is crucial for extracting optical quadratures in quantum optics experiments.
• Accurate homodyne angle control is essential due to ubiquitous fluctuations.
• Existing homodyne angle locking techniques have limited operational ranges, hindering full-state tomography.

Purpose of the Study:

• To develop a novel homodyne angle locking technique for continuous full-state tomography.
• To overcome the limitations of existing methods that cause discontinuities in tomography.
• To enable advanced quantum protocols like backaction evasion.

Main Methods:

• A universally tunable modulator was employed to generate error signals.
• The technique was demonstrated to produce high-quality error signals at arbitrary homodyne angles.
• The method allows for continuous operation across the required range for tomography.

Main Results:

• The new technique successfully generates high-quality error signals over an arbitrary homodyne angle range.
• This overcomes the discontinuity issue present in previous methods.
• Continuous full-state tomography is now achievable.

Conclusions:

• The presented homodyne angle locking technique significantly advances quantum state tomography.
• It enables continuous measurement of optical quadratures without discontinuities.
• This work is foundational for implementing time-varying homodyne angles in quantum experiments and backaction evasion protocols.