Quantum Registers

Dominique Unruh

University of Tartu




Abstract: We study quantum registers, i.e., parts of a quantum system on which we can operate individually. A quantum register could represent a variable in a quantum program, or a part of a physical quantum system, or a wire in a quantum circuit. While at the first glance, it may seem intuitively obvious what a register is (simply a factor in a tensor product), it is non-obvious what a register is formally. We present a general definition of registers (a "register category") that has classical and quantum registers as special cases. We show how this notion of registers enables powerful operations on registers (such as pairs, complements) and captures many concepts that tend to be used in informal reasoning.