Showing papers by "Yu-xi Liu published in 2006"
TL;DR: The essential role of the demon is explicitly demonstrated in this macroscopic QHE, which requires three steps: thermalization, quantum measurement, and quantum feedback controlled by the Maxwell demon.
Abstract: We study a new quantum heat engine (QHE), which is assisted by a Maxwell's demon. The QHE requires three steps: thermalization, quantum measurement, and quantum feedback controlled by the Maxwell demon. We derive the positive-work condition and operation efficiency of this composite QHE. Using controllable superconducting quantum circuits as an example, we show how to construct our QHE. The essential role of the demon is explicitly demonstrated in this macroscopic QHE.
141 citations
TL;DR: This proposed method avoids fast changes of either qubit frequencies or the amplitudes of the bias magnetic fluxes through the qubit loops, and also offers a remarkable way to implement any logic gate, as well as tomographically measure flux qubit states.
Abstract: We propose an experimentally realizable method to control the coupling between two flux qubits. In our proposal, the bias fluxes are always fixed for these two inductively coupled qubits. The detuning of these two qubits can be initially chosen to be sufficiently large, so that their initial interbit coupling is almost negligible. When a variable frequency or time-dependent magnetic flux (TDMF) is applied to one of the qubits, a well-chosen frequency of the TDMF can be used to compensate the initial detuning and to couple two qubits. This proposed method avoids fast changes of either qubit frequencies or the amplitudes of the bias magnetic fluxes through the qubit loops, and also offers a remarkable way to implement any logic gate, as well as tomographically measure flux qubit states.
123 citations
TL;DR: By conditionally rotating, one by one, selected Josephson-charge qubits, it is shown that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated.
Abstract: Going beyond the entanglement of microscopic objects (such as photons, spins, and ions), here we propose an efficient approach to produce and control the quantum entanglement of three macroscopic coupled superconducting qubits. By conditionally rotating, one by one, selected Josephson-charge qubits, we show that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated. The existence of GHZ correlations between these qubits could be experimentally demonstrated by effective single-qubit operations followed by high-fidelity single-shot readouts. The possibility of using the prepared GHZ correlations to test the macroscopic conflict between the noncommutativity of quantum mechanics and the commutativity of classical physics is also discussed.
110 citations
TL;DR: The motion of the NAMR, including if it is quantum mechanical or not, could be probed by detecting the voltage-fluctuation spectrum of the TLR, which is indirectly coupled to theNAMR via a controllable Josephson qubit acting as a quantum transducer.
Abstract: We propose a spectroscopic approach to probe tiny vibrations of a nanomechanical resonator (NAMR), which may reveal classical or quantum behavior depending on the decoherence-inducing environment. Our proposal is based on the detection of the voltage-fluctuation spectrum in a superconducting transmission line resonator (TLR), which is indirectly coupled to the NAMR via a controllable Josephson qubit acting as a quantum transducer. The classical (quantum mechanical) vibrations of the NAMR induce symmetric (asymmetric) Stark shifts of the qubit levels, which can be measured by the voltage fluctuations in the TLR. Thus, the motion of the NAMR, including if it is quantum mechanical or not, could be probed by detecting the voltage-fluctuation spectrum of the TLR.
95 citations
TL;DR: In this paper, the authors proposed a coupling method between a superconducting qubit and a data bus that uses a controllable time-dependent electromagnetic field (TDEF). But the TDEF was not applied to the qubit, but to a "dressed qubit" (i.e., qubit plus the electromagnetic field) which can be coupled to the data bus.
Abstract: We study a coupling (decoupling) method between a superconducting qubit and a data bus that uses a controllable time-dependent electromagnetic field (TDEF). As in recent experiments, the data bus can be either an LC circuit or a cavity field. When the qubit and the data bus are initially fabricated, their detuning should be made far larger than their coupling constant, so these can be treated as two independent subsystems. However, if a TDEF is applied to the qubit, then a "dressed qubit" (i.e., qubit plus the electromagnetic field) can be formed. By choosing appropriate parameters for the TDEF, the dressed qubit can be coupled to the data bus and, thus, the qubit and the data bus can exchange information with the assistance of the TDEF. This mechanism allows the scalability of the circuit to many qubits. With the help of the TDEF, any two qubits can be selectively coupled to (and decoupled from) a common data bus. Therefore, quantum information can be transferred from one qubit to another.
87 citations
TL;DR: In this article, the authors proposed a mechanism to interface a transmission line resonator with a nanomechanical resonator by coupling them to a charge qubit, a Cooper-pair box with a controllable gate voltage.
Abstract: We propose a mechanism to interface a transmission line resonator (TLR) with a nanomechanical resonator (NAMR) by commonly coupling them to a charge qubit, a Cooper-pair box with a controllable gate voltage. Integrated in this quantum transducer or simple quantum network, the charge qubit plays the role of a controllable quantum node coherently exchanging quantum information between the TLR and NAMR. With such an interface, a quasiclassical state of the NAMR can be created by controlling a single-mode classical current in the TLR. Alternatively, a "Cooper pair" coherent output through the transmission line can be driven by a single-mode classical oscillation of the NAMR.
77 citations
TL;DR: It is found that quantum computation based on cluster states is a promising approach for solid-state qubits.
Abstract: We propose a method to efficiently generate cluster states in charge qubits, both semiconducting and superconducting, as well as flux qubits. We show that highly entangled cluster states can be realized by a ``one-touch'' entanglement operation by tuning gate bias voltages for charge qubits. We also investigate the robustness of these cluster states for nonuniform qubits, which are unavoidable in solid-state systems. We find that quantum computation based on cluster states is a promising approach for solid-state qubits.
74 citations
TL;DR: In this article, the authors proposed a two-qubit coupling scheme where two or more flux qubits with different eigenfrequencies share Josephson junctions with a coupler loop devoid of its own quantum dynamics.
Abstract: We propose a coupling scheme where two or more flux qubits with different eigenfrequencies share Josephson junctions with a coupler loop devoid of its own quantum dynamics. Switchable two-qubit coupling is realized by tuning the frequency of the ac magnetic flux through the coupler to a combination frequency of two of the qubits. The coupling allows any or all of the qubits to be simultaneously at the degeneracy point and can change sign.
52 citations
TL;DR: In this article, the authors propose an efficient approach to prepare EPR pairs in currently existing Josephson nanocircuits with capacitive couplings, where two-qubit logic gates can be easily implemented while, strictly speaking, single qubit gates cannot be easily realized.
Abstract: We propose an efficient approach to prepare Einstein-Podolsky-Rosen (EPR) pairs in currently existing Josephson nanocircuits with capacitive couplings. In these fixed coupling circuits, two-qubit logic gates could be easily implemented while, strictly speaking, single-qubit gates cannot be easily realized. For a known two-qubit state, conditional single-qubit operation could still be designed to evolve only the selected qubit and keep the other qubit unchanged; the rotation of the selected qubit depends on the state of the other one. These conditional single-qubit operations allow us to deterministically generate the well-known Einstein-Podolsky-Rosen pairs, represented by EPR-Bell (or Bell) states. Quantum-state tomography is further proposed to experimentally confirm the generation of these states. The decays of the prepared EPR pairs are analyzed using numerical simulations. Possible application of the generated EPR pairs to test Bell's Inequality is also discussed.
47 citations
TL;DR: In this article, the interaction between two quantized optical fields and a cyclic atomic ensemble driven by a classic optical field was studied, and it was shown that the quantum information can be completely transferred from one quantised optical mode to another, and that quantum information carried by the two quantum fields can be stored in the collective modes of this atomic ensemble by adiabatically controlling the classic field Rabi frequencies.
Abstract: We systematically study the interaction between two quantized optical fields and a cyclic atomic ensemble driven by a classic optical field. This so-called atomic cyclic ensemble consists of three-level atoms with $\ensuremath{\Delta}$-type transitions due to the symmetry breaking, which can also be implemented in the superconducting quantum circuit by Yu-xi Liu et al. [Phys. Rev. Lett. 95, 087001 (2005)]. We explore the dynamic mechanisms to creating the quantum entanglements among photon states, and between photons and atomic collective excitations by the coherent manipulation of the atom-photon system. It is shown that the quantum information can be completely transferred from one quantized optical mode to another, and the quantum information carried by the two quantized optical fields can be stored in the collective modes of this atomic ensemble by adiabatically controlling the classic field Rabi frequencies.
19 citations
Journal Article•
TL;DR: Li, Li Zheng, Yu-xi Liu, and C. P. Sun as mentioned in this paper, have proposed a method to solve the problem of energy minimization in the context of energy-efficient energy management.
Abstract: Yong Li, Li Zheng, Yu-xi Liu, and C. P. Sun* Institute of Theoretical Physics & Interdisciplinary Center of Theoretical Studies, Chinese Academy of Sciences, Beijing, 100080, China College of Information Science and Engineering, Dalian Institute of Light Industry, Dalian, 116034, China Frontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan Received 19 October 2005; published 18 April 2006