Generation of four-photon polarization entangled decoherence-free states with cross-Kerr nonlinearity

Abstract

We propose a theoretical protocol for preparing four-photon polarization entangled decoherence-free states, which are immune to the collective noise. With the assistance of the cross-Kerr nonlinearities, a two-photon spatial entanglement gate, two controlled-NOT gates, a four-photon polarization entanglement gate are inserted into the circuit, where X homodyne measurements are aptly applied. Combined with some swap gates and simple linear optical elements, four-photon polarization entangled decoherence-free states which can be utilized to represent two logical qubits, |0〉L and |1〉L are achieved at the output ports of the circuit. This generation scheme may be implemented with current experimental techniques.

Encoding scheme using quantum dots for single logical qubit information onto four-photon decoherence-free states

“…In various quantum information processing schemes, quantum entanglement (main resource) can be easily attenuated by the influence of the environment-system. To solve this issue, the concept of a decoherencefree subspace [32][33][34][35][43][44][45][50][51][52][59][60][61] has been widely employed in quantum communications [86][87][88][89] and quantum computations [90][91][92] for robustness against collective decoherence [32][33][34] . In this paper, we proposed the encoding scheme, which consisted of the generation of four-photon decoherence-free states, and the encoding process to encode arbitrary quantum information onto logical qubits, using QD-cavity systems for single logical qubit information.…”

“…(2) In Refs. 43,52 , they overlooked the affections of decoherence effect 8,9,[12][13][14]21 in controlled gates using XKNLs.…”

“…Thus, the applications of a four-qubit decoherence-free subspace have been designed for increasing the maintenance of coherent quantum information. For the generations of four-qubit decoherence-free state, many researchers have exploited various resources, such as spontaneous parametric down conversions (SPDC) 46 , 47 or source of entangled state 48 , 49 with linear optics, Zeno-like measurements and post-selections 50 , cavity-QED 44 , 51 , and cross-Kerr nonlinearities (XKNLs) 52 , 53 .…”

“…For robust quantum information processing against collective decoherence, due to uncontrolled coupling between a system and the environment, the utilization of logical qubits {|0 L �, |1 L �} based on a decoherence-free subspace has been proposed [32][33][34] . Thus, one of the proposed concepts [32][33][34][35][43][44][45][50][51][52][59][60][61] for logical qubits is the design of four-qubit decoherence-free states 44,[50][51][52] , as follows:…”

Optical scheme for generating hyperentanglement having photonic qubit and time-bin via quantum dot and cross-Kerr nonlinearity

“…For the generation of hyperentanglement, our scheme includes nonlinearly optical devices and linearly optical apparatuses, used as follows. Nonlinear parts : (1) The QD-cavity system is used in the interaction between photons and an excess electron of QD confined in a single-sided cavity 20 , 33 – 40 , and (2) The parity gate (polarization entanglexr) uses XKNLs, quantum bus beams, and photon-number-resolving measurement 60 , 67 , 72 – 74 . Linear parts : (1) The time-bin encoder uses circularly polarizing beam splitters (CPBS) and a delayed loop (DL), and (2) Another time-bin encoder uses Pockels cells (PCs) 10 , 16 , 20 , 23 , 75 .…”