An unknown unitary gates, which is secretly chosen from several known ones, can always be distinguished perfectly. In this paper, we implement such a task on IBM's quantum processor. More precisely, we experimentally demonstrate the discrimination of two qubit unitary gates, the identity gate and the 2 3 π-phase shift gate, using two discrimination schemes -the parallel scheme and the sequential scheme. We program these two schemes on the ibmqx4, a 5-qubit superconducting quantum processor via IBM cloud, with the help of the QSI modules [S. Liu et al., arXiv:1710.09500, 2017. We report that both discrimination schemes achieve success probabilities at least 85%.
I. INTRODUCTIONThe discrimination of quantum operations asks to identify an unknown quantum operation from a set of known ones. As a fundamental task in quantum information and computation, many interesting aspects have been discovered over the last two decades, see [1-9] (and references therein) for a partial list. As applications, the discrimination of quantum operations plays important roles in the design of classical data hiding protocols [5] and the study of quantum reading capacity [10].The discrimination protocol is a step-by-step procedure consisting of (the unknown) operation evaluations, along with quantum state preparations, additional quantum operations and measurements. The goal is to output the identity of the given operations, based on the measurement results. Comparing to the discrimination of quantum states, the discrimination of quantum operations admits more freedoms. To see this, we note that quantum operations are reusable, which enables quantum entanglement to be capitalized in the discrimination protocols. In addition, ancillary systems are generally necessary for the optimal discrimination of two quantum operations. The perfect distinguishability of unitary operations [1] and quantum measurement apparatus [2], relies crucially on these aspects.On the other hand, quantum operations can be used in many fundamental different ways, such as in parallel or in sequential. A parallel (discrimination) scheme enables the unknown quantum operation to be performed in parallel, which can be viewed as a direct generalization of the quantum state discrimination with multiple i.i.