Preparation of three- and four-qubit decoherence-free states via Zeno-like measurements

Abstract

Enlightened by the idea of purification through Zeno-like measurements (Nakazato et al 2003 Phys. Rev. Lett. 90 060401), we propose a scheme for generating three- and four-qubit decoherence-free states with respect to collective amplitude damping. The whole system is in a star configuration of a spin network and the outer spin qubits construct the decoherence-free state via measuring the state of central spin qubit at intervals of τ repeatedly. An interesting feature is found: namely, that in order to prepare the three-qubit decoherence-free state successfully, the value of τ for the projected time-evolution operator must be set definitely, while this restrictive condition is relaxed for achieving the four-qubit decoherence-free state. The simulation results reveal that the fidelity approaches one asymptotically, and the corresponding success probability reaches a stable value by increasing the number of measurements N.

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.…”

“…From the comparison with the previous works, we can demonstrate the advantages of our scheme, as follows: (1) In Refs. 21,43 , they designed to generate threequbit decoherence-free states, and encode an arbitrary quantum information, but logical three-qubit 21,22,[36][37][38][39][40][41][42][43]50,60,93 could provide only the minimal immunity against collective decoherence. By this limited effect, the extending dimension of subsystem is obviously required.…”

“…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:…”

Generalized interaction-free evolutions

“…In this context, subradiant [11][12][13][14][15][16][17] as well decoherence-free (DF) states [19][20][21] have gained wide attention leading to unitary system dynamics. Several papers indeed have appeared in the last twenty years concerning the preparation of such states immune from decoherence in different physical contexts [22][23][24][25]. At the same time, starting from the idea that decoherence can be avoided remaining inside special subspaces that are protected from the interaction with the environment, the theory of DF subspaces and subsystems has been developed, see for example the review of Lidar and Whiley and references therein [26][27][28].…”

Preparation and entanglement purification through two-step measurements

“…In consideration of the decoherence caused by the environment, this method still works [23,24]. In recent years, this method has been extended to the continuous spectrum situation [25,26].…”