摘要：We consider an open quantum system of 𝑁 not directly interacting spins (qubits) in contact with both local and collective thermal environments. The
qubit-environment interactions are energy conserving. We trace out the variables
of the thermal environments and 𝑁−2 qubits to obtain the time-dependent reduced
density matrix for two arbitrary qubits. We numerically simulate the reduced
dynamics and the creation of entanglement (concurrence) as a function of
the parameters of the thermal environments and the number of qubits, 𝑁. Our results demonstrate that the two-qubit entanglement generally decreases as 𝑁 increases.
We show analytically that, in the limit 𝑁→∞, no entanglement can be
created. This indicates that collective thermal environments cannot create two-qubit
entanglement when many qubits are located within a region of the size of the
environment coherence length. We discuss possible relevance of our consideration
to recent quantum information devices and biosystems.
