Alternative scheme of universal optical programmable multi-qubit gates for polarization qubits

We propose an alternative scheme for programmable quantum gates specifically designed for polarization qubits of single photons. Unlike the conventional approach based on the scheme of Reck et al., we adopt the Hilbert-space expansion technique to enable a novel feature in the design of arbitrary quantum operations. We present a scheme that independently programs each matrix element of an operator. The proposed scheme can support the realization of many kinds of quantum operations. In anticipation of advances in the current quantum photonics technology, we assume the manipulation and detection of many photon qubits and propose a theoretical scheme to achieve n-polarization-qubit optical reconfigurable quantum gates by linear optical elements.