Search

We investigate the preservation of quantum coherence and entanglement carried by the three non-interacting qubits during their evolution in the presence of an external fluctuating field characterized by a classical Gaussian noise. Initially, the three non-interacting qubits are considered in two different maximally entangled states, namely Greenberger–Horne–Zeilinger ( X G ) and Werner (X W) state. Besides this, we study the time evolution of the two states in three different schemes, namely: common, mixed, and independent system–environment couplings. By deploying different measures, we show that the system–environment coupling and the Gaussian noise greatly affected the quantum correlation and coherence. We also found that the non-local correlation and coherence remain more dominant and robust in common system–environment coupling for the X G state under the Gaussian noise. Hence, this kind of feature of the X G state is a vital resource for the transmission of quantum information with reduced loss. [ABSTRACT FROM AUTHOR]

The monogamy of quantum entanglement captures the property of limitation in the distribution of entanglement. Various monogamy relations exist for different entanglement measures that are important in quantum information processing. Our goal in this work is to propose general monogamy inequalities for several entanglement measures on entangled qubit systems. The present results provide a unified model for various entanglement measures including the concurrence, the negativity, the entanglement of formation, Tsallis-q entropy, Rényi-q entropy, and Unified-(q, s) entropy. We then propose tightened monogamy inequalities for multipartite qubit systems and derive upper bounds of aforementioned entanglement measures for multipartite pure state under generalized bipartitions. We finally prove a generic result that most of tripartite high-dimensional entangled pure states have no entanglement monogamy. These results are useful for exploring the entanglement theory, quantum information processing and secure quantum communication. [ABSTRACT FROM AUTHOR]

Superdense coding is a distinct property of quantum entanglement. In this paper, we show that the bipartite three-particle W state can transmit 3 bits by sending two qubits using single qubit operations. This has justified previous conjecture (Agrawal and Pati, Phys. Rev. A 74(6), 062320 2006). Similar result holds for hyperentangled W states. [ABSTRACT FROM AUTHOR]

Toffoli gates are natural elements for the circuit model based quantum computation. We investigate general resource requirements for arbitrary n-qubit Toffoli gate. These resources consist of the nontrivial Clifford gate (CNOT), non-Clifford gate ( T gate), ancillary qubits, and circuit depth. To implement n-qubit Toffoli gates, we consider two cases: only one auxiliary qubit and unlimited auxiliary qubits. The key of the first case is to decompose an n-qubit Toffoli gate into the reduced Toffoli gate modulo phase shift using the Clifford gates and one ancillary qubit. With this construction, it only requires O( n) number of general resources for an n-qubit Toffoli gate. For the second case, an approximate Toffoli gate is constructed to obtain efficient decomposition of a Toffoli gate. The new decomposition can further reduce general resources except auxiliary qubits. [ABSTRACT FROM AUTHOR]

The ability to prepare arbitrary quantum state is the holy grail of quantum information technology. Previous schemes focus on circuit complexity using implicit decomposition schemes for global evolutions and are difficult in quantum experiments because the generation circuit can be completed for given coefficients each time. One protocol is firstly proposed in this paper in order to deterministically generate arbitrary four-qubit states with any coefficients. In order to complete this scheme with present physical techniques, we present an explicit quantum circuit with unknown coefficients of prepared states using elementary quantum gates. The key of our scheme is constructing the Cartan KAK decomposition of special transformations in $$SO(4)$$ and $$SO(8)$$ . And then, this protocol is extended to arbitrary five-qubit states and six-qubit states. [ABSTRACT FROM AUTHOR]

Two schemes via different entangled resources as the quantum channel are proposed to realize remote preparation of an arbitrary four-particle $$\chi $$ -state with high success probabilities. To design these protocols, some useful and general measurement bases are constructed, which have no restrictions on the coefficients of the prepared states. It is shown that through a four-particle projective measurement and two-step three-particle projective measurement under the novel sets of mutually orthogonal basis vectors, the original state can be prepared with the probability 50 and 100 %, respectively. And for the first scheme, the special cases of the prepared state that the success probability reaches up to 100 % are discussed by the permutation group. Furthermore, the present schemes are extended to the non-maximally entangled quantum channel, and the classical communication costs are calculated. [ABSTRACT FROM AUTHOR]

In this work, novel schemes for joint remote state preparation are presented, which involve N senders and 2 receivers as well as N senders and 3 receivers. The receivers can simultaneously reconstruct different qubit states containing the joint information from all senders. Compared with the protocols proposed by Su et al. (Int J Quantum Inf 10:1250006 (), the information of the prepared states in our schemes is distributed in a different way. Our protocols can be applied not only to states with real parameters but also ones with complex parameters. Moreover, the N-to-2 protocol is suitable for general qubit states besides equatorial states, and the receivers need not to perform any measurements and CNOT gates to reconstruct the states. [ABSTRACT FROM AUTHOR]

In this paper, we show that some special mixed quantum resource experience the same property of pure entanglement such as Bell state for quantum teleportation. It is shown that one mixed state and three bits of classical communication cost can be used to teleport one unknown qubit compared with two bits via pure resources. The schemes are easily implement with model physical techniques. Moreover, these resources are also optimal and typical for faithfully remotely prepare an arbitrary qubit, two-qubit and three-qubit states with mixed quantum resources. Our schemes are completed as same as those with pure quantum entanglement resources except only 1 bit additional classical communication cost required. The success probability is independent of the form of the mixed resources. [ABSTRACT FROM AUTHOR]

The cluster state has its feasibility for universal quantum computations. In this paper, we show that one symmetric cluster state can be used for the teleportation of an arbitrary two-qubit state deterministically. The one takes use of generalized Bell basis measurement while the other is completed using a general projective measurement from constructed orthogonal measurement basis and the Pauli flip measurement. Moreover, this state can also be utilized for remotely preparation of a restricted two qubit state within two different quantum network topologies, the controlled and jointed forms. Finally its capability for dense coding is investigated and shown n+3 classical bits transmissions by sending only n+1 qubits. [ABSTRACT FROM AUTHOR]

Immeasurability of a quantum state has important consequence in practical implementation of quantum computers. Our purpose is to analyze the efficiency of the entangled output of Pati-Braunstein deleting machine or Wootters-Zurek quantum copying machine as a quantum channel. Interestingly we find that for special values of the input parameter the state does not violate the Bell's inequality. Moreover, we analyze the performances of the entangled output of Pati-Braunstein deleting after the Wootters-Zurek copying machine. [ABSTRACT FROM AUTHOR]

In this paper, we propose two schemes to remotely split an arbitrary three-qubit state. The χ and a GHZ state are used to construct the quantum channel. One scheme is completed by using the generalized Bell basis measurement of multi-particles. The other scheme is constructed by using the quantum primitives, which are described by the quantum circuit and photon architecture. [ABSTRACT FROM AUTHOR]

Our purpose in this paper, is to show that several senders can jointly prepare a five-qubit Brown-state to a remote receiver. By constructing some useful measurement bases, we first present two schemes to prepare an arbitrary Brown-state with real coefficients or complex coefficients via the same quantum channel. Then, by using the permutation group the success probability is improved. Finally, the present schemes are generalized to multi-sender. [ABSTRACT FROM AUTHOR]

Our purpose in this paper, is to show that several senders can jointly prepare a four-qubit | χ〉-state to a remote receiver. By constructing some useful measurement bases, we first present two schemes to prepare an arbitrary | χ〉-state with real coefficients or complex coefficients via the same quantum channel. Then, by using the permutation group the success probability is improved. Finally, the present schemes are generalized to multi-sender. [ABSTRACT FROM AUTHOR]

Motivated by some previous joint remote preparation schemes, we first propose some quantum circuits and photon circuits that two senders jointly prepare an arbitrary one-qubit state to a remote receiver via GHZ state. Then, by constructing KAK decomposition of some transformation in SO(4), one quantum circuit is constructed for jointly preparing an arbitrary two-qubit state to the remote receiver. Furthermore, some deterministic schemes of jointly preparing one-qubit and two-qubit states are presented. Besides, the proposed schemes are extended to multi-sender and the partially entangled quantum resources. [ABSTRACT FROM AUTHOR]