We present the first experimental implementation of Direct Quantum Process Tomography. Direct tomography uses ideas from quantum error correction to reduce the number of experimental configurations required to characterize a quantum process.
As the method to completely characterize quantum dynamical processes, quantum process tomography (QPT) is vitally important for quantum information processing and quantum control, where the faithfulness of quantum devices plays an essential role. Here via weak measurements, we present a new QPT scheme characterized by its directness and parallelism. Comparing with the existing schemes, our scheme needs a simpler state preparation and much fewer experimental setups. Furthermore, each parameter of the quantum process is directly determined from only five experimental values in our scheme, meaning that our scheme is robust against the accumulation of errors.
We experimentally implement direct characterization of quantum dynamics (DCQD) algorithm of a single qubit proposed in M. Mohseni and D. A. Lidar [Phys. Rev. Lett. 97, 170501 (2006)], which does not require quantum state tomography. The number of experimental configurations is reduced by a factor of 2 compared with that of standard quantum process tomography, which can be increased four times with an ideal Bell state analyzer. We combine the DCQD algorithm with maximum-likelihood estimation to give the physical characterization of quantum dynamics. It can also be applied to obtaining partial information about quantum dynamics.
We report on the implementation of a quantum process tomography technique known as direct characterization of quantum dynamics applied on coherent and incoherent single-qubit processes in a system of trapped (40)Ca(+) ions. Using quantum correlations with an ancilla qubit, direct characterization of quantum dynamics reduces substantially the number of experimental configurations required for a full quantum process tomography and all diagonal elements of the process matrix can be estimated with a single setting. With this technique, the system's relaxation times T(1) and T(2) were measured with a single experimental configuration. We further show the first, complete characterization of single-qubit processes using a single generalized measurement realized through multibody correlations with three ancilla qubits.