Programmable quantum-state discriminator by nuclear magnetic resonance (8 pages)

J. Zhang, Gui‐Lu Long

Isaac L. Chuang

Tata Gopinath, Ranabir Das, Anil Kumar

A programmable quantum-state discriminator is implemented by using nuclear magnetic resonance. We use a two-qubit spin-$1∕2$ system, one for the data qubit and one for the ancilla (program) qubit. This device does the unambiguous (error-free) discrimination of a pair of states of the data qubit that are symmetrically located about a fixed state. The device is used to discriminate both linearly polarized states and elliptically polarized states. The maximum probability of successful discrimination is achieved by suitably preparing the ancilla qubit. It is also shown that the probability of discrimination depends on the angle of the unitary operator of the protocol and ellipticity of the data qubit state.

David G. Cory, Mark D. Price, Timothy F. Havel

Xue Fei, Du Jiang-Feng, Zhou Xian-Yi +2 more

We study the discrimination of quantum states from the other way around, i.e. the likeness of two quantum states. The fidelity is used to describe the likeness of two quantum states. Then we present a scheme to obtain the fidelity of two unknown qubits directly from the integral area of the spectra of the assistant qubit (spin) on a nuclear-magnetic-resonance quantum information processor. Finally, we demonstrate the scheme on a three-qubit quantum information processor. The experimental data are consistent with the theoretical expectation with an average error of 0.05, which confirms the scheme.

Chuck Easttom