arXiv subjects

Tiantian Huan

Publications and source records attributed to Tiantian Huan.

5 recordsLinked to original sources

arXiv2021

Distributed entanglement generation from asynchronously excited qubits

The generation of GHZ states calls for simultaneous excitation of multiple qubits. The peculiarity of such states is reflected in their nonzero distributed entanglement which is not contained in other entangled states. We study the optimal way to excite three superconducting qubits through a common cavity resonator in a circuit such that the generation of distributed entanglement among them could be obtained at the highest degree in a time-controllable way. A non-negative measure quantifying this entanglement is derived as a time function of the quadripartite system evolution. We find that this measure does not stay static but obtains the same maximum periodically. When the qubit-resonator couplings are allowed to vary, its peak value is enhanced monotonically by increasing the greatest coupling strength to one of the qubits. The period of its peak to peak revival maximizes when the couplings become inhomogeneous, thus qubit excitation becoming asynchronous, at a relative ratio of 0.35. The study demonstrates the role of asynchronous excitations for time-controlling multi-qubit systems, in particular in extending entanglement time.

quant-ph↗

arXiv2020

Ramsey-biased spectroscopy of superconducting qubits under dispersion

We proposed a spectroscopic method that extends Ramsey's atomic spectroscopy to detect the transition frequency of a qubit fabricated on a superconducting circuit. The method uses a multi-interval train of qubit biases to implement an alternate resonant and dispersive couplings to an incident probe field. The consequent absorption spectrum of the qubit has a narrower linewidth at its transition frequency than that obtained from constantly biasing the qubit to resonance while the middle dispersive evolution incurs only a negligible shift in detected frequency. Modeling on transmon qubits, we find that the linewidth reduction reaches 23% and Ramsey fringes are simultaneously suppressed at extreme duration ratio of dispersion over resonance for a double-resonance scheme. If the scheme is augmented by an extra resonance segment, a further 37% reduction can be achieved.

quant-ph↗

arXiv2020

Synchronization of two cavity-coupled qubits measured by entanglement

Some nonlinear radiations such as superfluorescence can be understood as cooperative effects between atoms. We regard the cooperative radiation as a manifested effect secondary to the intrinsic synchronization among the atoms and propose a time-resolved measure of synchronization on a cavity-coupled dual-qubit system using multipartite concurrence. Comparing the variation of the concurrence over time with that of an asynchronicity measure, we find that the synchronization between the qubits features a time delay characteristic to the initiation of superfluorescent pulses. The delay coincides with the duration for the qubits to establish cooperation and emit the collective radiation, after which the concurrence monotonically increases to a stationary value while the asynchronicity dives to a steady minimum. Furthermore, the establishment of synchronization is determined by the qubit-cavity coupling strength. Asynchronicity shows that synchronization is only possible when the coupling enters strong regime and sustains to a high level when the coupling becomes ultra-strong.

quant-ph↗

arXiv2020

Evolution of Skyrmion Crystals in Fe$_{0.5}$Co$_{0.5}$Si-Like Quasi-Two-Dimensional Ferromagnets Driven by External Magnetic Field and Temperature

Magnetic skyrmions have attracted great research interest in recent years due to their exotic physical properties, scientific merit and potential applications in modern technology. Here, we apply a quantum computational method to investigate the spin configurations of Fe$_{0.5}$Co$_{0.5}$Si-Like quasi-two-dimensional ferromagnetic system with co-existence of Dzyaloshinsky-Moriya and Heisenberg exchange interactions. We find that within a weak magnetic field perpendicular to the film plane, skyrmion crystal (SkX) of hexagonal-close-packed pattern can be induced, the spin configurations evolve with applied magnetic field and temperature. This quantum model, if scaled, is able to qualitatively reproduce the experimental results of SkX with long periodicity, especially, when the skyrmion size is around a few nano-meters in diameter, it is expected to be more accurate than the classical ones.

cond-mat.mes-hall↗

arXiv2015

Dynamic entanglement transfer in a double-cavity optomechanical system

We give a theoretical study of a double-cavity system in which a mechanical resonator beam is coupled to two cavity modes on both sides through radiation pressures. The indirect coupling between the cavities via the resonator sets up a correlation in the optomechanical entanglements between the two cavities with the common resonator. This correlation initiates an entanglement transfer from the intracavity photon-phonon entanglements to an intercavity photon-photon entanglement. Using numerical solutions, we show two distinct regimes of the optomechanical system, in which the indirect entanglement either builds up and eventually saturates or undergoes a death-and-revival cycle, after a time lapse for initiating the cooperative motion of the left and right cavity modes.

quant-ph↗