Input-output Theory Research Articles

Detections of the Atomic States via the Phase Shifts of Transmitted Photons Through a Cavity

We propose an approach to detect an unknown quantum state of the atom(s) by measuring the phase shifts of the transmitted photons through a dispersively-coupled cavity. In the framework of the input-output theory, we derive the relations between the phase shifts of the transmitted photons and the states of the atom(s) in the cavity. It is shown that due to the dispersive interaction between the cavity and the atom(s), information about the atomic state can then be extracted by measuring the phase shifts of the transmitted photons through the cavity. The feasibility of the proposal is also discussed with the experimental parameters by numerical method.

Generation of the quadripartite Greenberger–Horne–Zeilinger entangled state in quantum beat lasers

In this letter, a scheme is presented to obtain quadripartite Greenberger–Horne–Zeilinger (GHZ) entanglement via quantum beats in a four-level diamond configuration atomic system. When the top and the ground states are initially prepared in a coherent superposition, the four quantized fields coupling with four dipole-allowed transitions can be correlated with each other by using a strong microwave field to drive the dipole-forbidden transition. It is the combined effect of atomic coherence-controlled correlated-spontaneous emission and double quantum beats that results in the quadripartite GHZ-type entanglement. Our numerical results show that the quadripartite entanglement, which can be controlled effectively by varying the amplitude and phase of the microwave field, occurs in a very wide parameter range. In addition, using input–output theory, we find that the output quadripartite entanglement is robust against thermal fluctuations, which may be useful for long-distance quantum communications.

Quantum input-output theory for optical cavities with arbitrary coupling strength: Application to two-photon wave-packet shaping

We develop quantum-optical input-output theory for resonators with arbitrary coupling strength, and for input fields whose spectrum can be wider than the cavity free-spectral range, while ensuring that the field-operator commutator relations in space-time variables are correct. The cavity-field commutator exhibits a series of space-time echoes, representing causal connections of certain space-time points by light propagation. We apply the theory to two-photon wave-packet shaping by cavity reflection, which displays a remarkable illustration of dispersion cancellation. We also show that the theory is amenable to inclusion of intracavity absorbing and emitting atoms, allowing, for example, dissipative losses within the cavity to be incorporated in a quantum mechanically correct way.

Input-output theory for waveguide QED with an ensemble of inhomogeneous atoms

We study the collective effects that emerge in waveguide quantum electrodynamics where several (artificial) atoms are coupled to a one-dimensional superconducting transmission line. Since single microwave photons can travel without loss for a long distance along the line, real and virtual photons emitted by one atom can be reabsorbed or scattered by a second atom. Depending on the distance between the atoms, this collective effect can lead to super- and subradiance or to a coherent exchange-type interaction between the atoms. Changing the artificial atoms transition frequencies, something which can be easily done with superconducting qubits (two levels artificial atoms), is equivalent to changing the atom-atom separation and thereby opens the possibility to study the characteristics of these collective effects. To study this waveguide quantum electrodynamics system, we extend previous work and present an effective master equation valid for an ensemble of inhomogeneous atoms driven by a coherent state. Using input-output theory, we compute analytically and numerically the elastic and inelastic scattering and show how these quantities reveal information about collective effects. These theoretical results are compatible with recent experimental results using transmon qubits coupled to a superconducting one-dimensional transmission line [A.~F.~van Loo {\it et al.}].

Input-output theory of the unconventional photon blockade

We study the unconventional photon blockade, recently proposed for a coupled-cavity system, in presence of input and output quantum fields. Mixing of the input or output channels still allows strong photon antibunching of the output field, but for optimal values of the system parameters that differ substantially from those that maximize antibunching of the intracavity field. This result shows that the specific input-output geometry in a photonic system determines the optimal design in view of single-photon device operation. We provide a compact analytical formula that allows finding the optimal parameters for each specific system geometry.

PASSIVITY-BASED PARAMETER ESTIMATION AND COMPOSITE ADAPTIVE POSITION CONTROL OF INDUCTION MOTORS

In the rotor reference frame, the input-output linearization theory was adopted to decouple the rotor position and rotor flux. We then designed two adaptation laws to estimate the rotor resistance and mechanical parameters of the motor. The passive properties of the negative feedback connection from the rotor flux observer to the rotor resistance estimator, and the position controller were analyzed according to the passivity theorem. The overall control system was proved to be globally stable. Finally, experimental results show that the proposed scheme is robust to the variations of the rotor resistance and load torque disturbances. Furthermore, the estimated parameters can converge to the actual values.

ENVIRON: Environmental Impacts from Advanced Communications - Evidence from an Input-Output Theory

The ENVIRON model estimates environmental impacts (positive, negative) from the introduction and use of Advanced Communications (AC); Information Society Technologies (IST) in industrial, commercial and business sectors in Greece. The model estimates effects on output, employment, income, environment and energy requirements. It is based on the: (i) Leontief Input-Output theory-analysis, (ii) Introduction of AC/IST and in particular of the Telematics as a new sector into the economic system of a country, and (iii) Incorporation of pollution emission factors into the system. The types of AC represented are grouped into six categories: access to information systems, electronic transactions, robotics and tele-action, tele-working, mobile communications and video facilities. Industry sectors considered are transport, business and services, public and domestic. The application of ENVIRON indicates that the introduction of AC into the production process will result into a 15.8% decrease of energy consumption, a reduction of 14.32-10.14% in SO2, and it will have strong positive effects on the economic system of Greece especially on profits related to environmental protection. The model demonstrates the use of the Leontief Input-Output analysis in environmental impacts analysis matters and policy.

Passivity-Based Parameter Estimation and Position Control of Induction Motors via Composite Adaptation

This paper proposes the parameters estimation and position control of an induction motor drive by using the composite adaptation scheme. First, in the rotor reference frame, the input-output linearization theory was employed to decouple the mechanical rotor position and the rotor flux amplitude at the transient state. An open-loop current model rotor flux observer was utilized for estimating the flux, and then the adaptive laws for estimating the rotor resistance, moment of inertia, viscous friction coefficient, and load torque. The passive properties of the flux observer, rotor resistance estimator, and composite adaptive position controller were analyzed based on the passivity theorem. According to the properties, the overall position control system was proved to be globally stable without using Lyapunov-type arguments. Experimental results are finally provided to show that the proposed method is robust to variations of the motor mechanical parameters, rotor resistance, and load torque disturbances. Moreover, good position tracking response and characteristics on parameter estimation can be achieved.

Inelastic Microwave Photon Scattering off a Quantum Impurity in a Josephson-Junction Array

Quantum fluctuations in an anharmonic superconducting circuit enable frequency conversion of individual incoming photons. This effect, linear in the photon beam intensity, leads to ramifications for the standard input-output circuit theory. We consider an extreme case of anharmonicity in which photons scatter off a small set of weak links within a Josephson junction array. We show that this quantum impurity displays Kondo physics and evaluate the elastic and inelastic photon scattering cross sections. These cross sections reveal many-body properties of the Kondo problem that are hard to access in its traditional fermionic version.

Intracavity Tunneling Introduced Transparency in Ultrastrong-coupling Regime

Intracavity tunneling induced transparency in asymmetric double-quantum wells embedded in a microcavity in the ultrastrong-coupling regime is investigated by the input-output theory developed by Ciuti and Carusotto. In this system a narrow spectra can be realized under anti-resonant terms of the external dissipation. Fano-interference asymmetric line profile is found in the absorption spectra.

Analysis of Embodied Energy Consumption and Greenhouse Gas (GHG) Emissions in Chinese Manufacturing Industry

This paper attempts to discuss the embodied energy consumption and embodied greenhouse gas emissions in manufacturing industry. Based the on input-output theory, this paper establishes the calculation model, which gives the calculation of embodied energy consumption and embodied greenhouse gas emissions of 2002 and 2007 respectively. By comparison, it draws the conclusion that the total direct energy consumption of 2007 is much more than the year of 2002, while the total embodied energy consumption is less than the year of 2002. However, Non-metallic mineral products, Metal smelting and pressing and Electric equipment and machinery perform otherwise. The reason accounting for the calculation results is that the embodied energy intensity is greatly decreased.

Radio Frequency Charge Parity Meter

We demonstrate a total charge parity measurement by detecting the radio frequency signal that is reflected by a lumped-element resonator coupled to a single InAs nanowire double quantum dot. The high frequency response of the circuit is used to probe the effects of the Pauli exclusion principle at interdot charge transitions. Even parity charge transitions show a striking magnetic field dependence that is due to a singlet-triplet transition, while odd parity transitions are relatively insensitive to a magnetic field. The measured response agrees well with cavity input-output theory, allowing accurate measurements of the interdot tunnel coupling and the resonator-charge coupling rate g(c)/2π~17 MHz.

Gain, directionality, and noise in microwave SQUID amplifiers: Input-output approach

We present a new theoretical framework to analyze microwave amplifiers based on the dc SQUID. Our analysis applies input-output theory generalized for Josephson junction devices biased in the running state. Using this approach, we express the high-frequency dynamics of the SQUID as a scattering between the participating modes. This enables us to elucidate the inherently nonreciprocal nature of gain as a function of bias current and input frequency. This method can, in principle, accommodate an arbitrary number of Josephson harmonics generated in the running state of the junction. We report detailed calculations taking into account the first few harmonics that provide simple semiquantitative results showing a degradation of gain, directionality, and noise of the device as a function of increasing signal frequency. We also discuss the fundamental limits on device performance and applications of this formalism to real devices.

Creating multimode squeezed states and Greenberger-Horne-Zeilinger entangled states using atomic coherent effects

We propose a scalable scheme for a unitary multimode operator using an optical cavity with an atomic ensemble. We exemplify three-mode and four-mode cases and engineer the squeeze operators that are decoupled from the atomic degrees of freedom. The squeeze parameters can be large since they are proportional to the number of atoms. Using the input-output theory we show that ideal squeezed states and perfect squeezing could be approached at the output. At the same time, we show that it is possible to obtain tripartite and quadripartite Greenberger-Horne-Zeilinger entangled states for continuous variables. The responsible mechanism for both the multimode squeezing and the genuine multipartite entanglement is based on the atomic coherence controlled parametric interactions. The scalability of the scheme is simply obtained by including more transitions in the atomic system.

All-cavity electromagnetically induced transparency and optical switching: Semiclassical theory

The transmission of a probe field experiencing electromagnetically induced transparency and optical switching in an atomic medium enclosed in an optical cavity is investigated. Using a semiclassical input-output theory for the interaction between an ensemble of four-level atoms and three optical cavity fields coupled to the same spatial cavity mode, we derive the steady-state transmission spectra of the probe field and discuss the dynamics of the intracavity field buildup. The analytical and numerical results are in good agreement with recent experiments with ion Coulomb crystals [M. Albert et al., Nature Photon. 5, 633 (2011)].

Two-color continuous-variable quantum entanglement in a singly resonant optical parametric oscillator

We apply the input-output theory of optical cavities to formulate a quantum treatment of a continuous-wave singly resonant optical parametric oscillator. This case is mainly relevant to highly nondegenerate signal and idler modes. We show that both intensity and quadrature squeezing are present and that the maximum noise reduction below the standard quantum limit is the same at the signal and idler frequencies as in the doubly resonant case. As the threshold of oscillation is approached, however, the intensity-difference and quadrature spectra display a progressive line narrowing which is absent in the balanced doubly resonant case. By use of the separability criterion for continuous variables, the signal-idler state is found to be entangled over wide ranges of the parameters. We show that attainable levels of squeezing and entanglement make singly resonant configurations ideal candidates for two-color quantum information processes, because of their ease of tuning in experimental realizations.

DYNAMICS AND EXTRACTION OF QUANTUM DISCORD IN A MULTIPARTITE OPEN SYSTEM

We consider a multipartite system consisting of two noninteracting qubits each embedded in a single-mode leaky cavity, in turn connected to an external bosonic reservoir. Initially, we take the two qubits in an entangled state while the cavities and the reservoirs have zero photons. We investigate, in this six-partite quantum system, the transfer of quantum discord from the qubits to the cavities and reservoirs. We show that this transfer also occurs when the cavities are not entangled. Moreover, we discuss how quantum discord can be extracted from the cavities and transferred to distant systems by traveling leaking photons, using the input–output theory.

Input-Output Analysis: Theory and Foundations (Análise de Insumo-Produto: Teoria e Fundamentos)

This paper presents, in Portuguese, an overview of the input-output theory, originally developed by Wassily Leontief. The first and second chapters present the background of the theory of input-output, placing the work of Leontief in a historical view. Chapter 3 presents the basic theory of input-output. Chapter 4 deals with how the input-output data is overall processed and disseminated by the statistical agencies, and specifically by the Brazilian statistical office (IBGE), and how this information can be analyzed to allow the system to work with the original Leontief model. Chapter 5 deals with how the original Leontief model, developed for a national economy can be extended to the analysis of regional economies, either for a single region or for several interconnected regions. Chapter 6 presents the basic methods of analysis used with input-output models. Chapter 7 deals with the use of input-output in modeling environmental issues. The discussion of how input-output matrices can be obtained by using census and non-census methods is made in Chapter 8. Finally, Chapter 9 aims to present the various possible applications of input-output analysis, while at the same time, outlining the possible future paths in terms of using this powerful tool of analysis.

Scheme to generate three-mode continuous-variable entanglement in cavity quantum electrodynamics

We propose a theoretical method of generating a three-mode continuous-variable entanglement in an optical cavity with an atomic cloud. The scheme uses Raman transitions between stable atomic ground states and under the input–output theory a three-mode entangled light of the output fields can be produced. The characters of the tripartite entanglement, the degree of the quadrature-phase amplitude correlations among the three modes are discussed by applying a sufficient inseparability criterion for multipartite continuous-variable entanglement, which was proposed by van Loock and Furusawa. The dependences of the correlation on the effective coupling constants are theoretically analyzed.

Linear System Control via Dynamic Saturating Actuators

The problem of controlling systems via saturating actuators is addressed. In most previous studies the actuator is represented by a simple saturation. However, there are practical situations where such simple model is insufficient. Then, the actuator dynamics must be accounted for. Presently, a more convenient model is used that takes into account both the dynamics and the saturation of the actuator. A saturated output feedback controller is then developed for the whole ‘actuator-plant’ system, using a backstepping-like design technique. The closed-loop system is analyzed using the input-output stability theory. Sufficient conditions are thus established that guarantee the closed-loop stability and the fact that both the actuator and the controller stop saturating after a finite transient period, implying perfect tracking of the output reference signal provided this is compatible with the actuator constraint.