Distinguishability of hyperentangled Bell states by linear evolution and local projective measurement

Neal C. Pisenti, Carl Philipp E. Gaebler, and Theresa W. Lynn

Physical Review A 84 (2011) 22340


Measuring an entangled state of two particles is crucial to many quantum communication protocols. Yet Bell- state distinguishability using a finite apparatus obeying linear evolution and local measurement is theoretically limited. We extend known bounds for Bell-state distinguishability in one and two variables to the general case of entanglement in *n* two-state variables. We show that at most :mil:`2^{n+1} – 1` classes out of :mil:`4^{n}` hyper-Bell states can be distinguished with one copy of the input state. With two copies, complete distinguishability is possible. We present optimal schemes in each case.