Multicopy Adaptive Local Discrimination: Strongest Possible Two-Qubit Nonlocal Bases.

Area of Science:

• Quantum Information Science
• Quantum Computing
• Quantum Communication

Background:

• Composite quantum states can exhibit nonlocality, necessitating global operations for optimal discrimination.
• Adaptive local schemes can perfectly distinguish N pairwise orthogonal pure states using N-1 copies.

Purpose of the Study:

• To identify orthonormal bases in two-qubit Hilbert space requiring more than N-1 copies for adaptive discrimination.
• To analyze the general case of multi-copy adaptive local distinguishability for orthogonal ensembles.
• To explore ensembles with discrimination requirements differing between adaptive local and separable schemes.

Main Methods:

• Construction of specific orthonormal bases in two-qubit Hilbert space.
• Analysis of multi-copy adaptive local distinguishability for orthogonal ensembles.
• Comparison of discrimination requirements for adaptive local versus adaptive separable schemes.

Main Results:

• Demonstrated two-qubit orthonormal bases whose adaptive discrimination requires three copies.
• Provided a general analysis of multi-copy adaptive local distinguishability, assigning nonlocal strengths to ensembles.
• Identified ensembles requiring fewer copies for discrimination under adaptive separable schemes than adaptive local schemes.

Conclusions:

• The nonlocal strength of composite quantum states varies, impacting discrimination requirements.
• The findings have direct applications in multipartite secret sharing tasks.
• Indicated a novel superadditivity phenomenon related to locally accessible information.