Chemisorption of nitronyl-nitroxide radicals on gold surface: an assessment of morphology, exchange interaction and decoherence time.

A combined Tof-SIMS, XPS and STM characterization has been adopted here to study the deposition of a sulphur-functionalized nitronyl nitroxide radical on Au(111) clearly demonstrating the chemisorption of intact molecules....

Relative entropy for von Neumann subalgebras

We revisit the connection between index and relative entropy for an inclusion of finite von Neumann algebras. We observe that the Pimsner–Popa index connects to sandwiched [Formula: see text]-Rényi relative entropy for all [Formula: see text], including Umegaki’s relative entropy at [Formula: see text]. Based on that, we introduce a new notation of relative entropy to a subalgebra which generalizes subfactors index. This relative entropy has application in estimating decoherence time of quantum Markov semigroups.

DECOHERENCE-FREE STORAGE INFORMATION SPACE

Quantum systems are of great interest in current realities. Quantum computers are not an alternative to the classic. Rather, they can be attributed to the class of devices specializing in a separate group of tasks. However, a key issue in the design of quantum computers is the issue of decoherence time. To combat that phenomenon, various methods of isolating a quantum system are being developed, including the use of extremely low temperatures and high vacuum. In addition, one of the ways to combat decoherence is to use dark states, due to the fact that a system of atoms in this state is not able to interact with light – absorb or emit photons. In this paper, various systems of three-level atoms are considered. Schemes of two types of atoms are represented graphically – λ-atoms, v-atoms. The concept of a dark quantum state and the concept of a family of a quantum state are introduced. An algorithm for finding the dimension and basis of the subspace of dark states is presented. According to the algorithm, the dimensions and bases of the subspaces of dark states in these systems are calculated.

The influences of the dispersion and impurity on the properties of the Gaussian confining potential qubit with magnetic field

The influences of the dispersion, the impurity and the electron–phonon coupling (EPC) on the properties of the Gaussian confining (GC) potential qubit with magnetic field were studied by Pekar-type variation method. Results show that the decoherence time will increase with increasing the dielectric constant (DC) ratio, the dispersion coefficient and the EPC strength, respectively. The phase rotation quality factor increases with increasing the dielectric constant ratio, the dispersion coefficient and EPC strength, respectively. The magnetic field has a regulatory effect on the decoherence time and the phase rotation quality factor.

Investigating the lower bound of minimum gate times using optimal control

Motivated by a bound derived in a recent work [C. Arenz, B. Russell, D. Burgarth and H. Rabitz, New J. Phys. 19 (2017) 103015], we apply optimal control theory to the dynamics of qubit systems, with the goal of investigating the lower bound of minimum gate times. In practice, we not only need to reach the desired unitary gates but we need to do so in a reasonable time (below the typical decoherence time). Therefore, we employ the recently introduced lower bound to estimate the minimum gate time and resort to numerical gate optimization in order to study the tightness of the obtained bound and our findings verify the relationship between the internal Hamiltonian and the minimum evolution time remarkably well. Finally, we discuss both challenges and ways forward for obtaining the same efficacy under realistic conditions.

niSWAP and NTCP gates realized in a circuit QED system

Based on superconducting qubit coupled to a resonator driven by a strong microwave field, we propose a method to implement two quantum logic gates ([Formula: see text]SWAP and NTCP gates) of one qubit simultaneously controlling [Formula: see text] qubits selected from [Formula: see text] qubits in a circuit QED [Formula: see text] by introducing qubit–qubit interaction. The interaction between the qubits and the circuit QED can be achieved by tuning the gate voltage and the external flux. The operation times of the logic gates are much smaller than the decoherence time and dephasing time. Moreover, the numerical simulation under the influence of the gates operations shows that the scheme could be achieved efficiently with presently available techniques.

Dynamics of measurement-induced nonlocality of quantum states in a structured environment

In this paper, we analyze the dynamics of the measurement-induced nonlocality (MIN) of two-qubit states undergoing decoherence induced by a structured environment modeled as a collection of simple harmonic oscillators. For the Markovian dynamics, MIN and the concurrence decrease monotonically with the scaled time and the decoherence time of the former is longer than that of the latter. While for the non-Markovian dynamics, MIN can revive for finite time periods after its disappearance immediately. With a comparison, the concurrence can revive for finite time periods after its complete disappearance which lasts for some time. The MIN takes a zero value for some discrete time points while the concurrence takes a zero value for finite time periods. In this sense, we can say that the MIN is more robust than the concurrence to decoherence. Finally, the non-Markovianity measure has been examined and we find that the strong non-Markovianity of the dynamical process corresponds to a large amplitude of the revival of MIN and the concurrence.