arXiv subjects

M. Feng

Publications and source records attributed to M. Feng.

At least 37 records · Page 2Linked to original sources

arXiv2017

Optimal joint measurements of complementary observables by a single trapped ion

The uncertainty relations, pioneered by Werner Heisenberg nearly 90 years ago, set a fundamental limitation on the joint measurability of complementary observables. This limitation has long been a subject of debate, which has been reignited recently due to new proposed forms of measurement uncertainty relations. The present work is associated with a new error trade-off relation for compatible observables approximating two incompatible observables, in keeping with the spirit of Heisenberg's original ideas of 1927. We report the first \textsl{direct} test and confirmation of the tight bounds prescribed by such an error trade-off relation, based on an experimental realisation of optimal joint measurements of complementary observables using a single ultracold $^{40}Ca^{+}$ ion trapped in a harmonic potential. Our work provides a prototypical determination of ultimate joint measurement error bounds with potential applications in quantum information science for high-precision measurement and information security.

quant-ph↗

arXiv2015

Exploring the quantum critical behaviour in a driven Tavis-Cummings circuit

Quantum phase transitions play an important role in many-body systems and have been a research focus in conventional condensed matter physics over the past few decades. Artificial atoms, such as superconducting qubits that can be individually manipulated, provide a new paradigm of realising and exploring quantum phase transitions by engineering an on-chip quantum simulator. Here we demonstrate experimentally the quantum critical behaviour in a highly-controllable superconducting circuit, consisting of four qubits coupled to a common resonator mode. By off-resonantly driving the system to renormalise the critical spin-field coupling strength, we have observed a four-qubit non-equilibrium quantum phase transition in a dynamical manner, i.e., we sweep the critical coupling strength over time and monitor the four-qubit scaled moments for a signature of a structural change of the system's eigenstates. Our observation of the non-equilibrium quantum phase transition, which is in good agreement with the driven Tavis-Cummings theory under decoherence, offers new experimental approaches towards exploring quantum phase transition related science, such as scaling behaviours, parity breaking and long-range quantum correlations.

quant-ph↗

arXiv2014

Homogeneous Linewidth Narrowing of the Charged Exciton via Nuclear Spin Screening in an InAs/GaAs Quantum Dot Ensemble

In semiconductor quantum dots, the electron hyperfine interaction with the nuclear spin bath is the leading source of spin decoherence at cryogenic temperature. Using high-resolution two-color differential transmission spectroscopy, we demonstrate that such electron-nuclear coupling also imposes a lower limit for the positively charged exciton dephasing rate, γ, in an ensemble of InAs/GaAs quantum dots. We find that the dephasing rate is sensitive to the strength of the hyperfine interaction, which can be controlled through the application of an external magnetic field in the Faraday configuration. At zero applied field, strong electron-nuclear coupling induces additional dephasing beyond the radiative limit and γ= 230 MHz (0.95 μeV). Screening of the hyperfine interaction is achieved for an external field of ~1 T, resulting in γ= 172 MHz (0.71 μeV) limited only by spontaneous recombination. On the other hand, application of a Voigt magnetic field mixes the spin eigenstates, which increases the dephasing rate by up to 75%. These results are reproduced with a simple and intuitive model that captures the essential features of the electron hyperfine interaction and its influence on γ.

cond-mat.mes-hall↗

arXiv2014

Parity symmetry and parity breaking in the quantum Rabi model with addition of Ising interaction

We explore the possibility to generate new parity symmetry in the quantum Rabi model after a bias is introduced. In contrast to a mathematical treatment in a previous publication [J. Phys. A 46, 265302 (2013)], we consider a physically realistic method by involving an additional spin into the quantum Rabi model to couple with the original spin by an Ising interaction. The rule can be found that the parity symmetry is broken by introducing a bias and then restored by adding new degrees of freedom. Experimental feasibility of realizing the models under discussion is investigated.

quant-ph↗

arXiv2013

Parity breaking and scaling behavior in light-matter interaction

The light-matter interaction described by Rabi model and Jaynes-Cummings (JC) model is investigated by parity breaking as well as the scaling behavior of ground-state population-inversion expectation. We show that the parity breaking leads to different scaling behaviors in the two models, where the Rabi model demonstrates scaling invariance, but the JC model behaves in cusp-like way. Our study helps further understanding rotating-wave approximation and could present more subtle physics than any other characteristic parameter for the difference between the two models. More importantly, our results could be straightforwardly applied to the understanding of quantum phase transitions in spin-boson model. Furthermore, the scaling behavior is observable using currently available techniques in light-matter interaction.

quant-ph↗

arXiv2013

Preservation of quantum correlation between separated nitrogen-vacancy centers embedded in photonic crystal cavities

We investigate the non-Markovian dynamics of quantum correlation between two initially entangled nitrogen-vacancy centers (NVC) embedded in photonic crystal cavities (PCC). We find that a finite quantum correlation is preserved even asymptotically when the transition frequency of the NVC is within the band gap of the PCC, which is quantitatively different from the result of approaching zero under the Born-Markovian approximation. In addition, once the transition frequency of NVC is far beyond the band gap of the PCC, the quantum correlation initially prepared in NVC will be fully transferred to the reservoirs in the long-time limit. Our result reveals that the interplay between the non-Markovian effect of the structured reservoirs and the existence of emitter-field bound state plays an essential role in such quantum correlation preservation. This feature may open new perspectives for devising active decoherence-immune solid-state optical devices.

quant-ph↗

arXiv2012

Quantum simulation of artificial Abelian gauge field using nitrogen-vacancy center ensembles coupled to superconducting resonators

We propose a potentially practical scheme to simulate artificial Abelian gauge field for polaritons using a hybrid quantum system consisting of nitrogen-vacancy center ensembles (NVEs) and superconducting transmission line resonators (TLR). In our case, the collective excitations of NVEs play the role of bosonic particles, and our multiport device tends to circulate polaritons in a behavior like a charged particle in an external magnetic field. We discuss the possibility of identifying signatures of the Hofstadter "butterfly" in the optical spectra of the resonators, and analyze the ground state crossover for different gauge fields. Our work opens new perspectives in quantum simulation of condensed matter and many-body physics using hybrid spin-ensemble circuit quantum electrodynamics system. The experimental feasibility and challenge are justified using currently available technology.

quant-ph↗

arXiv2012

Quantum-memory-assisted entropic uncertainty principle under noise

The measurement outcomes of two incompatible observables on a particle can be precisely predicted when it is maximally entangled with a quantum memory, as quantified recently [Nature Phys. 6, 659 (2010)]. We explore the behavior of the uncertainty relation under the influence of local unital and nonunital noisy channels. While the unital noises only increase the amount of uncertainty, the amplitude-damping nonunital noises may amazingly reduce the amount of uncertainty in the long-time limit. This counterintuitive phenomenon could be justified by different competitive mechanisms between quantum correlations and the minimal missing information after local measurement.

quant-ph↗

arXiv2011

High-fidelity quantum memory using nitrogen-vacancy center ensemble for hybrid quantum computation

We study a hybrid quantum computing system using nitrogen-vacancy center ensemble (NVE) as quantum memory, current-biased Josephson junction (CBJJ) superconducting qubit fabricated in a transmission line resonator (TLR) as quantum computing processor and the microwave photons in TLR as quantum data bus. The storage process is seriously treated by considering all kinds of decoherence mechanisms. Such a hybrid quantum device can also be used to create multi-qubit W states of NVEs through a common CBJJ. The experimental feasibility and challenge are justified using currently available technology.

quant-ph↗

arXiv2010

Three dimensional cooling and detecting of a nanosphere with a single cavity

We propose an experimental scheme to cool and measure the three-dimensional (3D) motion of an optically trapped nanosphere in a cavity. Driven by three lasers on TEM00, TEM01, and TEM10 modes, a single cavity can cool a trapped nanosphere to the quantum ground states in all three dimensions under the resolved-sideband condition. Our scheme can also detect an individual collision between a single molecule and a cooled nanosphere efficiently. Such ability can be used to measure the mass of molecules and the surface temperature of the nanosphere. We also discuss the heating induced by the intensity fluctuation, pointing instability, and the phase noise of lasers, and justify the feasibility of our scheme under current experimental conditions.

quant-ph↗

arXiv2010

Entanglement of separate nitrogen-vacancy centers coupled to a whispering-gallery mode cavity

We present a quantum electrodynamical model involving nitrogen-vacancy centers coupled to a whispering-gallery mode cavity. Two schemes are considered to create W state and Bell state, respectively. One of the schemes makes use of the Raman transition with the cavity field virtually excited; The other enables the Bell state preparation and quantum information transfer by virtue of dark state evolution and adiabatic passage, which is tolerant to ambient noise and experimental parameter fluctuations. We justify our schemes by considering the experimental feasibility and challenge using currently available technology.

quant-ph↗

arXiv2010

Dissipative dynamics of quantum discord under quantum chaotic environment

We investigate the dissipative dynamics of quantum discord in a decoherence model with two initially entangled qubits in addition to a quantum kicked top. The two qubits are uncoupled during the period of our study and one of them interacts with the quantum kicked top. We find that the long time behavior of quantum discord could be well described by the fidelity decay of the quantum kicked top; for short time behavior, however, the phase of the amplitude of the fidelity decay is necessary to provide more specific information about the system. We have made comparison between the quantum kicked top and multi-mode oscillator system in describing environment, and also compared the dynamics of the entanglement with that of quantum discord.

quant-ph↗

arXiv2010

Entanglement preservation for multilevel systems under non-ideal pulse control

We investigate how to effectively preserve the entanglement between two noninteracting multilevel oscillators coupled to a common reservoir under non-ideal pulse control. A universal characterization using fidelity is developed for the behavior of the system based on Nakajima-Zwanzig projection operator technique. Our analysis includes the validity of the approximation method and the decoherence-suppression by the non-ideal pulse control. The power of our strategy for protecting entanglement is numerically tested, showing potential applications for quantum information processing.

quant-ph↗

arXiv2010

Proposed method for direct measurement of non-Markovian character of the qubits coupled to bosonic reservoirs

The non-Markovianity is a recently proposed characterization of the non-Markovian behavior in an open quantum system, based on which we first present a practical idea for directly measuring the non-Markovian character of a single qubit coupled to a zero-temperature bosonic reservoir, and then extend to investigate the dynamics of two noninteracting qubits subject to two reservoirs respectively with a lower bound of non-Markovianity. Our scheme, with no need of optimization procedures and quantum state tomography, is helpful for experimental implementation.

quant-ph↗

arXiv2009

Deterministically entangling distant nitrogen-vacancy centers by a nanomechanical cantilever

We present a practical scheme by global addressing to deterministically entangle negatively charged nitrogen-vacancy (N-V) centers in distant diamonds using a nano-mechanical cantilever with the magnetic tips strongly coupled to the N-V electron spins. Symmetric Dicke states are generated as an example, and the experimental feasibility and challenge of our scheme are discussed.

quant-ph↗

arXiv2009

The most generalized analytical approximation to the solution of single-mode spin-boson model without rotating-wave approximation

The single-mode spin-boson model (SMSBM) has extensive application in different subfields of physics. In the absence of rotating-wave approximation (RWA), we try to solve SMSBM analytically. We argue that the analytical expression obtained is the most exact approximation to the solution of the system under the assumption of Abel-Ruffini theorem, which works for a wide range of the parameters such as coupling strength and detuning and would be practical for currently available experiments.

quant-ph↗

arXiv2009

Nuclear spin qubits in a trapped-ion quantum computer

Physical systems must fulfill a number of conditions to qualify as useful quantum bits (qubits) for quantum information processing, including ease of manipulation, long decoherence times, and high fidelity readout operations. Since these conditions are hard to satisfy with a single system, it may be necessary to combine different degrees of freedom. Here we discuss a possible system, based on electronic and nuclear spin degrees of freedom in trapped ions. The nuclear spin yields long decoherence times, while the electronic spin, in a magnetic field gradient, provides efficient manipulation, and the optical transitions of the ions assure a selective and efficient initialization and readout.

quant-ph↗

arXiv2009

Sudden death and birth of entanglement beyond the Markovian approximation

We investigate the entanglement dynamics of two initially entangled qubits interacting independently with two uncorrelated reservoirs beyond the Markovian approximation. Quite different from the Markovian reservoirs [C. E. Lopez et al., Phys. Rev. Lett. 101 (2008) 080503], we find that entanglement sudden birth (ESB) of the two reservoirs occurs without certain symmetry with respect to the entanglement sudden death (ESD) of the two qubits. A phenomenological interpretation of entanglement revival is also given.

quant-ph↗