0605041v4

related topics
{states, state, optimal}
{key, protocol, security}
{let, theorem, proof}
{information, entropy, channel}
{error, code, errors}
{algorithm, log, probability}
{alice, bob, state}
{qubit, qubits, gate}

Invertible Quantum Operations and Perfect Encryption of Quantum States

Ashwin Nayak, Pranab Sen

abstract: In this note, we characterize the form of an invertible quantum operation, i.e., a completely positive trace preserving linear transformation (a CPTP map) whose inverse is also a CPTP map. The precise form of such maps becomes important in contexts such as self-testing and encryption. We show that these maps correspond to applying a unitary transformation to the state along with an ancilla initialized to a fixed state, which may be mixed. The characterization of invertible quantum operations implies that one-way schemes for encrypting quantum states using a classical key may be slightly more general than the ``private quantum channels'' studied by Ambainis, Mosca, Tapp and de Wolf (FOCS 2000). Nonetheless, we show that their results, most notably a lower bound of 2n bits of key to encrypt n quantum bits, extend in a straightforward manner to the general case.

oai_identifier:
oai:arXiv.org:quant-ph/0605041
categories:
quant-ph
comments:
9 pages. Version 3 has minor edits, a correction to Theorem 2.2, and a proof sketch.Author affiliation updated.Version 4 has an additional reference. To appear in QIC
arxiv_id:
quant-ph/0605041
created:
2006-05-03
updated:
2006-11-02

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