Certifiable Lower Bounds of Wigner Negativity Volume and Non-Gaussian Entanglement with Conditional Displacement...

Area of Science:

• Quantum Information Science
• Quantum Optics
• Quantum Computing

Background:

• Circuit and cavity quantum electrodynamics (QED) utilize qubits dispersively coupled to high-quality cavities.
• Characteristic functions of cavity states are probed using conditional displacement (CD) gates.
• Certifying non-Gaussian entanglement is crucial for advanced quantum technologies.

Purpose of the Study:

• Propose a novel method to certify non-Gaussian entanglement between cavities.
• Utilize only CD gates and qubit readouts for entanglement detection.
• Establish experimental bounds for non-Gaussianity and entanglement measures.

Main Methods:

• Leverage Bochner's theorem to connect Wigner function negativity and partial transpose negativity.
• Develop a conditional displacement (CD) witness for non-Gaussian entanglement.
• Measure characteristic function at specific points to detect entanglement.

Main Results:

• Demonstrate detection of non-Gaussian entanglement in states like entangled cats and photon-subtracted squeezed vacua.
• Show that the CD witness provides simultaneous lower bounds to Wigner negativity volume and a geometric entanglement measure.
• Achieve detection by measuring as few as four points of the characteristic function.

Conclusions:

• The proposed CD witness offers an experimentally accessible method for certifying non-Gaussian entanglement.
• This approach circumvents the need for full quantum state tomography.
• Provides practical lower bounds for key quantum information measures.