Universal superreplication of unitary gates

G Chiribella, Y Yang, C Huang - Physical review letters, 2015 - APS
Physical review letters, 2015APS
Quantum states obey an asymptotic no-cloning theorem, stating that no deterministic
machine can reliably replicate generic sequences of identically prepared pure states. In
stark contrast, we show that generic sequences of unitary gates can be replicated
deterministically at nearly quadratic rates, with an error vanishing on most inputs except for
an exponentially small fraction. The result is not in contradiction with the no-cloning theorem,
since the impossibility of deterministically transforming pure states into unitary gates …
Quantum states obey an asymptotic no-cloning theorem, stating that no deterministic machine can reliably replicate generic sequences of identically prepared pure states. In stark contrast, we show that generic sequences of unitary gates can be replicated deterministically at nearly quadratic rates, with an error vanishing on most inputs except for an exponentially small fraction. The result is not in contradiction with the no-cloning theorem, since the impossibility of deterministically transforming pure states into unitary gates prevents the application of the gate replication protocol to states. In addition to gate replication, we show that parallel uses of a completely unknown unitary gate can be compressed into a single gate acting on qubits, leading to an exponential reduction of the amount of quantum communication needed to implement the gate remotely.
American Physical Society
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