arXiv subjects

L. Tian

Publications and source records attributed to L. Tian.

26 records · Page 2Linked to original sources

arXiv2006

Correcting low-frequency noise with continuous measurement

Low-frequency noise presents a serious source of decoherence in solid-state qubits. When combined with a continuous weak measurement of the eigenstates, the low-frequency noise induces a second-order relaxation between the qubit states. Here we show that the relaxation provides a unique approach to calibrate the low-frequency noise in the time-domain. By encoding one qubit with two physical qubits that are alternatively calibrated, quantum logic gates with high fidelity can be performed.

quant-ph↗

arXiv2005

Quantum teleportation between nanomechanical modes

We study a quantum teleportation scheme between two nanomechanical modes without local interaction. The nanomechanical modes are linearly coupled to and connected by the continuous variable modes of a superconducting circuit consisting of a transmission line and Josephson junctions. We calculate the fidelity of transferring Gaussian states at finite temperature and non-unit detector efficiency. For coherent state, a fidelity above the classical limit of 1/2 can be achieved for a large range of parameters.

quant-ph↗

arXiv2004

Schroedinger Cat States of a Nanomechanical Resonator

We present a scheme of generating large-amplitude Schrödinger cat states and entanglement in a coupled system of nanomechanical resonator and single Cooper pair box (SCPB), without being limited by the magnitude of the coupling. It is shown that the entanglement between the resonator and the SCPB can be detected by a spectroscopic method.

quant-ph↗

arXiv2004

Scalable Ion Trap Quantum Computing without Moving Ions

A hybrid quantum computing scheme is studied where the hybrid qubit is made of an ion trap qubit serving as the information storage and a solid-state charge qubit serving as the quantum processor, connected by a superconducting cavity. In this paper, we extend our previous work [1] and study the decoherence, coupling and scalability of the hybrid system. We present our calculations of the decoherence of the coupled ion - charge system due to the charge fluctuations in the solid-state system and the dissipation of the superconducting cavity under laser radiation. A gate scheme that exploits rapid state flips of the charge qubit to reduce decoherence by the charge noise is designed. We also study a superconducting switch that is inserted between the cavity and the charge qubit and provides tunable coupling between the qubits. The scalability of the hybrid scheme is discussed together with several potential experimental obstacles in realizing this scheme.

quant-ph↗

arXiv2004

Coupled ion - nanomechanical systems

We study ions in a nanotrap, where the electrodes are nanomechanical resonantors. The ions play the role of a quantum optical system which acts as a probe and control, and allows entanglement with or between nanomechanical resonators.

quant-ph↗

arXiv2003

Projective Measurement Scheme for Solid-State Qubits

We present an effective measurement scheme for the solid-state qubits that does {\bf not} introduce extra decoherence to the qubits until the measurement is switched on by a resonant pulse. The resonant pulse then maximally entangles the qubit with the detector. The scheme has the feature of being projective, noiseless, and switchable. This method is illustrated on the superconducting persistent-current qubit, but can be applied to the measurement of a wide variety of solid-state qubits, the {\bf direct} detection of the electromagnetic signals of which gives poor resolution of the qubit states.

quant-ph↗

arXiv2003

Interfacing quantum optical and solid state qubits

We present a generic model of coupling quantum optical and solid state qubits, and the corresponding transfer protocols. The example discussed is a trapped ion coupled to a charge qubit (e.g. Cooper pair box). To enhance the coupling, and achieve compatibility between the different experimental setups we introduce a superconducting cavity as the connecting element.

quant-ph↗

arXiv2003

Optical pumping of quantum dot nuclear spins

An all-optical scheme to polarize nuclear spins in a single quantum dot is analyzed. The hyperfine interaction with randomly oriented nuclear spins presents a fundamental limit for electron spin coherence in a quantum dot; by cooling the nuclear spins, this decoherence mechanism could be suppressed. The proposed scheme is inspired by laser cooling methods of atomic physics and implements a "controlled Overhauser effect" in a zero-dimensional structure.

cond-mat.mes-hall↗