Quantum Bit Commitment can be Unconditionally Secure

It is generally believed that unconditionally secure quantum bit commitment is ruled out in principle by a “no-go theorem”. We point out that the theorem only establishes the existence of a cheating unitary operator in any scheme of quantum bit commitment, however there is no proof that the unitary operator is always known to the cheating party, hence it does not necessarily follow that quantum bit commitment is insecure. In this work, we propose a scheme where the cheating party cannot construct the required unitary operator because it depends on the other party’s unknown random choices; consequently the scheme is not breakable even with the help of a quantum computer. PACS numbers: 03.67.-a, 89.70.+c Typeset using REVTEX E-mail address: [email protected]