Highly efficient hyperentanglement concentration with two steps assisted by quantum swap gates

Area of Science:

• Quantum Information Science
• Quantum Communication
• Quantum Optics

Background:

• Hyperentanglement combines multiple degrees of freedom (e.g., polarization and spatial modes) in entangled quantum states.
• Concentrating entanglement is crucial for overcoming losses in long-distance quantum communication.
• Existing methods often struggle with efficiency and fidelity, especially for complex hyperentangled states.

Purpose of the Study:

• To develop an efficient two-step hyperentanglement concentration protocol (hyper-ECP) for polarization-spatial hyperentangled Bell states.
• To enhance the success probability of obtaining maximally hyperentangled states from partially entangled states.
• To improve the fidelity of quantum gate operations in the weak coupling regime.

Main Methods:

• Utilized a two-step protocol leveraging the high-capacity nature of hyperentanglement.
• Employed swap gates constructed with giant optical circular birefringence (GOCB) from a diamond nitrogen-vacancy (NV) center in a photonic crystal cavity.
• Transferred information between degrees of freedom (DOF) of photon systems to concentrate entanglement.

Main Results:

• Successfully demonstrated a hyper-ECP that significantly improves the success probability.
• Achieved the transfer of useful information between hyperentangled photon pairs, increasing the yield of maximally hyperentangled states.
• Showcased the possibility of high-fidelity quantum gate operations by mapping infidelities to heralded losses.

Conclusions:

• The proposed hyper-ECP offers a promising approach for enhancing the efficiency of quantum communication protocols.
• The use of NV-center-based swap gates provides a viable method for manipulating hyperentangled states.
• The protocol is robust, achieving high fidelity even under weak coupling conditions, paving the way for practical quantum networks.