Publication details
Universal NOT gate
| Authors | |
|---|---|
| Year of publication | 2000 |
| Type | Article in Periodical |
| Magazine / Source | J. Mod. Opt. |
| MU Faculty or unit | |
| Citation | |
| Web | http://xxx.lanl.gov/abs/quant-ph/9901053 |
| Field | Theoretical physics |
| Keywords | QUANTUM STATES; OPTIMAL CLONING; ENSEMBLES; QUBITS |
| Description | It is not a problem to complement a classical bit, i.e. to change the value of a bit, a 0 to a 1 and vice versa. This is accomplished by a NOT gate. Complementing a qubit in an unknown state, however, is another matter. We show that this operation cannot be done perfectly. We define the Universal-NOT (U-NOT) gate which out of N identically prepared pure input qubits generates M output qubits in a state which is as close as possible to the perfect complement. This gate can be realized by classical estimation and subsequent re-preparation of complements of the estimated state. Its fidelity is therefore equal to the fidelity F= (N+1)/(N+2) of optimal estimation, and does not depend on the required number of outputs. We also show that when some additional a priori information about the state of input qubit is available, than the fidelity of the quantum NOT gate can be much better than the fidelity of estimation. |
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