We investigate systems of spinless one-dimensional chiral fermions realized, e. g., in the arms of electronic Mach-Zehnder interferometers, at high energies. Taking into account the curvature of the fermionic spectrum and a finite interaction range, we find a new scattering mechanism where high-energy electrons scatter off plasmons (density excitations). This leads to an exponential decay of the single-particle Green's function even at zero temperature with an energy-dependent rate. As a consequence of this electron-plasmon scattering channel, we observe the coherent excitation of a plasmon wave in the wake of a high-energy electron resulting in the buildup of a monochromatic sinusoidal density pattern.
Resonant quantum gates in circuit quantum electrodynamics
G. Haack,
F. Helmer,
M. Mariantoni,
F. Marquardt,
E. Solano
Physical Review B
82
(2)
024514
(2010)
| Journal
| PDF
We propose the implementation of fast resonant gates in circuit quantum electrodynamics for quantum information processing. We show how a suitable utilization of three-level superconducting qubits inside a resonator constitutes a key tool to perform diverse two-qubit resonant gates, improving the operation speed when compared to slower dispersive techniques. To illustrate the benefit of resonant two-qubit gates in circuit quantum electrodynamics, we consider the implementation of a two-dimensional cluster state in an array of N x N superconducting qubits by using resonant controlled-phase and one-qubit gates, where the generation time grows linearly with N. For N = 3, and taking into account decoherence mechanisms, a fidelity over 60% for the generation of this cluster state is obtained.
Introduction to quantum noise, measurement, and amplification
A. A. Clerk,
M. H. Devoret,
S. M. Girvin,
Florian Marquardt,
R. J. Schoelkopf
Reviews of Modern Physics
82
(2)
1155-1208
(2010)
| Journal
| PDF
The topic of quantum noise has become extremely timely due to the rise of quantum information physics and the resulting interchange of ideas between the condensed matter and atomic, molecular, optical-quantum optics communities. This review gives a pedagogical introduction to the physics of quantum noise and its connections to quantum measurement and quantum amplification. After introducing quantum noise spectra and methods for their detection, the basics of weak continuous measurements are described. Particular attention is given to the treatment of the standard quantum limit on linear amplifiers and position detectors within a general linear-response framework. This approach is shown how it relates to the standard Haus-Caves quantum limit for a bosonic amplifier known in quantum optics and its application to the case of electrical circuits is illustrated, including mesoscopic detectors and resonant cavity detectors.
ac conductance through an interacting quantum dot
Bjoern Kubala,
Florian Marquardt
Physical Review B
81
(11)
115319
(2010)
| Journal
| PDF
We investigate the linear ac conductance for tunneling through an arbitrary interacting quantum dot in the presence of a finite dc bias. In analogy to the well-known Meir-Wingreen formula for the dc case, we are able to derive a general formula for the ac conductance. It can be expressed entirely in terms of local correlations on the quantum dot in the form of a Keldysh block diagram with four external legs. We illustrate the use of this formula as a starting point for diagrammatic calculations by considering the ac conductance of the noninteracting resonant-level model and deriving the result for the lowest order of electron-phonon coupling. We show how known results are recovered in the appropriate limits.
Single-atom cavity QED and optomicromechanics
M. Wallquist,
K. Hammerer,
P. Zoller,
C. Genes,
M. Ludwig,
F. Marquardt,
P. Treutlein,
J. Ye,
H. J. Kimble
In a recent publication [ K. Hammerer, M. Wallquist, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, P. Zoller, J. Ye, and H. J. Kimble, Phys. Rev. Lett. 103, 063005 ( 2009)] we have shown the possibility to achieve strong coupling of the quantized motion of a micron-sized mechanical system to the motion of a single trapped atom. In the proposed setup the coherent coupling between a SiN membrane and a single atom is mediated by the field of a high finesse cavity and can be much larger than the relevant decoherence rates. This makes the well-developed tools of cavity quantum electrodynamics with single atoms available in the realm of cavity optomechanics. In this article we elaborate on this scheme and provide detailed derivations and technical comments. Moreover, we give numerical as well as analytical results for a number of possible applications for transfer of squeezed or Fock states from atom to membrane as well as entanglement generation, taking full account of dissipation. In the limit of strong-coupling the preparation and verification of nonclassical states of a mesoscopic mechanical system is within reach.
Optimal control of circuit quantum electrodynamics in one and two
dimensions
R. Fisher,
F. Helmer,
S. J. Glaser,
F. Marquardt,
T. Schulte-Herbrueggen
Optimal control can be used to significantly improve multi-qubit gates in quantum information processing hardware architectures based on superconducting circuit quantum electrodynamics. We apply this approach not only to dispersive gates of two qubits inside a cavity, but, more generally, to architectures based on two-dimensional (2D) arrays of cavities and qubits. For high-fidelity gate operations, simultaneous evolutions of controls and couplings in the two coupling dimensions of cavity grids are shown to be significantly faster than conventional sequential implementations. Even under experimentally realistic conditions speedups by a factor of three can be gained. The methods immediately scale to large grids and indirect gates between arbitrary pairs of qubits on the grid. They are anticipated to be paradigmatic for 2D arrays and lattices of controllable qubits.
We provide a full quantum mechanical analysis of a weak energy measurement of a driven mechanical resonator. We demonstrate that measurements too weak to resolve individual mechanical Fock states can nonetheless be used to detect the nonclassical energy fluctuations of the driven mechanical resonator, i.e., "phonon shot noise". We also show that the third moment of the oscillator's energy fluctuations provides a far more sensitive probe of quantum effects than the second moment, and that measuring the third moment via the phase shift of light in an optomechanical setup directly yields the type of operator ordering postulated in the theory of full-counting statistics.
Entanglement of mechanical oscillators coupled to a nonequilibrium
environment
Max Ludwig,
K. Hammerer,
Florian Marquardt
Physical Review A
82
(1)
012333
(2010)
| Journal
| PDF
Recent experiments aim at cooling nanomechanical resonators to the ground state by coupling them to nonequilibrium environments in order to observe quantum effects such as entanglement. This raises the general question of how such environments affect entanglement. Here we show that there is an optimal dissipation strength for which the entanglement between two coupled oscillators is maximized. Our results are established with the help of a general framework of exact quantum Langevin equations valid for arbitrary bath spectra, in and out of equilibrium. We point out why the commonly employed Lindblad approach fails to give even a qualitatively correct picture.
Photon shuttle: Landau-Zener-Stuckelberg dynamics in an optomechanical system
Georg Heinrich,
J. G. E. Harris,
Florian Marquardt
Physical Review A
81
(1)
011801
(2010)
| Journal
| PDF
The motion of micro- and nanomechanical resonators can be coupled to electromagnetic fields. Such optomechanical setups allow one to explore the interaction of light and matter in a new regime at the boundary between quantum and classical physics. We propose an approach to investigate nonequilibrium photon dynamics driven by mechanical motion in a recently developed setup with a membrane between two mirrors, where photons can be shuttled between the two halves of the cavity. For modest driving strength we predict the possibility of observing an Autler-Townes splitting indicative of Rabi dynamics. For large drive, we show that this system displays Landau-Zener-Stueckelberg dynamics originally known from atomic two-state systems.
Contact
Theory Division Prof. Florian Marquardt
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
