By encoding quantum dynamics in a shared EPR entanglement and single qubit states, we propose a program- able quantum processor which allows us to implement local restricted set of operations on the remote state. Furthermore, we discuss an experimental demonstration of the programmable gate using linear optical elements.
We present a probabilistic quantum processor for qubits. The processor itself is represented by a fixed array of gates. The input of the processor is constituted by two registers. In the program register the set of instructions (program) is encoded. This program is applied to the data register. The processor we present can perform any operation on a single qubit with a certain probability. If the operation is unitary, the probability is in general 1/4, but for more restricted sets of operators the probability can be higher.
We experimentally demonstrate a programmable single-qubit quantum gate. This device applies a unitary phase shift operation to a data qubit with the value of the phase shift being fully determined by the state of a program qubit. Our linear optical implementation is based on the encoding of qubits into polarization states of single photons, two-photon interference on a polarizing beam splitter, and measurement on the output program qubit. We fully characterize the programmable gate by quantum process tomography. The achieved average quantum process fidelity exceeding 97% illustrates very good performance of the gate for all values of the encoded phase shift. We also show that by using a different set of program states the device can operate as a programmable partial polarization filter.
Quantum entanglement enables measurement on one party to affect the other’s state. Based on this peculiar feature, we propose a model of remote-controlled quantum computing and design an optical scheme to realize this model for a single qubit. As an experimental demonstration of this scheme, we further implement three Pauli operators, Hardmard gate, phase gate, and π / 8 gate. The minimal fidelity obtained by quantum process tomography reaches 82%. Besides, as a potential application, our model contributes to secure remote quantum information processing.