Abstract
We propose and experimentally verify a cooling limit for a quantum channel going through an incoherent environment. The environment consists of a large number of independent non-interacting and non-interfering elementary quantum systems – qubits. The qubits travelling through the channel can only be randomly replaced by environmental qubits. We investigate a conditional cooling limit that exploits an additional probing output. The limit specifies when the single-qubit channel is quantum, i.e. it preserves entanglement. It is a fundamental condition for entanglement-based quantum technology.
Highlights
We presented necessary conditions to preserve entanglement propagated through an incoherent environment
We showed that entanglement can be preserved using a local auxiliary projection even for a many-particle environment
For sufficient cooling of a thermal environment, these conditions are reduced to simple error-success ratios (3), (7)
Summary
To derive an unconditional cooling limit, we ignore the possibility of access by any auxiliary output in the environment. An environmental qubit is considered of the environment and pT in the state ≤ 1 is the. To derive the maximum of the probability pT (for thermal environment, a maximum of temperature T), we consider a maximally entangled state |Ψ−〉 =. Between the reference qubit and the channel qubit, written in the basis of the environmental state. The condition for pT represents a necessary criterion for the channel itself to be quantum, preserving entanglement. Where PS is the probability of successful transmission of the maximally entangled state. PS stands for the success probability of transmitting a pure singlet Ψ− Ψ− through the environment, and pT is the measure of error, represented by a random thermal excitation of an environmental qubit
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