Quantum impurity models coupled to Markovian and non-Markovian baths

We develop a method to study quantum impurity models, small interacting quantum systems bilinearly coupled to an environment, in the presence of an additional Markovian quantum bath, with a generic nonlinear coupling to the impurity. We aim at computing the evolution operator of the reduced density matrix of the impurity, obtained after tracing out all the environmental degrees of freedom. First, we derive an exact real-time hybridization expansion for this quantity, which generalizes the result obtained in the absence of the additional Markovian dissipation and which could be amenable to stochastic sampling through diagrammatic Monte Carlo. Then, we obtain a Dyson equation for this quantity and we evaluate its self-energy with a resummation technique known as the noncrossing approximation. We apply this novel approach to a simple fermionic impurity coupled to a zero temperature fermionic bath and in the presence of Markovian pump, losses, and dephasing

Quantum impurity models coupled to Markovian and non-Markovian baths

We develop a method to study quantum impurity models, small interacting quantum systems bilinearly coupled to an environment, in the presence of an additional Markovian quantum bath, with a generic nonlinear coupling to the impurity. We aim at computing the evolution operator of the reduced density matrix of the impurity, obtained after tracing out all the environmental degrees of freedom. First, we derive an exact real-time hybridization expansion for this quantity, which generalizes the result obtained in the absence of the additional Markovian dissipation and which could be amenable to stochastic sampling through diagrammatic Monte Carlo. Then, we obtain a Dyson equation for this quantity and we evaluate its self-energy with a resummation technique known as the noncrossing approximation. We apply this novel approach to a simple fermionic impurity coupled to a zero temperature fermionic bath and in the presence of Markovian pump, losses, and dephasing

Emergent finite frequency criticality of driven-dissipative correlated lattice bosons

Critical points and phase transitions are characterized by diverging susceptibilities, reflecting the tendency of the system toward spontaneous symmetry breaking. Equilibrium statistical mechanics bounds these instabilities to occur at zero frequency, giving rise to static order parameters. In this work we argue that a prototype model of correlated driven-dissipative lattice bosons, of direct relevance for upcoming generation of circuit QED arrays experiments, exhibits a susceptibility sharply diverging at a finite nonzero frequency, which is an emerging scale set by interactions and nonequilibrium effects. In the broken-symmetry phase the corresponding macroscopic order parameter becomes nonstationary and oscillates in time without damping, thus breaking continuous time-translational symmetry. Our work, connecting breaking of time translational invariance to divergent finite frequency susceptibilities, which are of direct physical relevance, could potentially be extended to study other time-domain instabilities in nonequilibrium quantum systems, including Floquet time crystals and quantum synchronization

Spectral functions and negative density of states of a driven-dissipative nonlinear quantum resonator

We study the spectral properties of Markovian driven-dissipative quantum systems, focusing on the nonlinear quantum van der Pol oscillator as a paradigmatic example. We discuss a generalized Lehmann representation, in which single-particle Green's functions are expressed in terms of the eigenstates and eigenvalues of the Liouvillian. Applying it to the quantum van der Pol oscillator, we find a wealth of phenomena that are not apparent in the steady-state density matrix alone. Unlike the steady state, the photonic spectral function has a strong dependence on interaction strength. Further, we find that the interplay of interaction and non-equilibrium effects can result in a surprising 'negative density of states', associated with a negative temperature, even in absence of steady state population inversion

A Transputer-based List Mode Parallel System For Digital Radiography With 2d Silicon Detectors

We believe that a dedicated parallel computer system can represent an effective and flexible approach to the problem of 'list mode' acquisition and reconstruction of digital radiographic images obtained with a double-sided silicon microstrip detector. We present a Transputer-based implementation of a parallel system for the data acquisition and image reconstruction from a silicon crystal with 200 mum read-out pitch. We are currently developing a prototype of the system connected to a detector with a 10 mm2 sensitive area

A TRANSPUTER-BASED LIST MODE PARALLEL SYSTEM FOR DIGITAL RADIOGRAPHY WITH 2D SILICON DETECTORS

We believe that a dedicated parallel computer system can represent an effective and flexible approach to the problem of 'list mode' acquisition and reconstruction of digital radiographic images obtained with a double-sided silicon microstrip detector. We present a Transputer-based implementation of a parallel system for the data acquisition and image reconstruction from a silicon crystal with 200 mum read-out pitch. We are currently developing a prototype of the system connected to a detector with a 10 mm2 sensitive area

Modular Data-acquisition System Based On Transputer Technology For Bi-dimensional Time Coincidence Counting

We describe the rationale and the test of a modular Data AcQuisition system (DAQ) for bi-dimensional (X-Y) digital imaging, based on a 16 channel Time-to-Digital Converter (TDC) NIM module connected to a specially designed TRAnsputer Module (TRAM). TDC time resolution is 12.5 ns (LSB) with a 40 MHz clock, time range is 3.3 s (28 bits), for a maximum rate of 500 kHz/channel guaranteed. The TDC + TRAM pair is the basic unit that can be scaled in modules of 8X + 8Y channels to meet the user's requirement for a larger number of X-Y channels to be considered simultaneously. TDC directly accesses the large RAM memory (32 Mbytes) of the INMOS T805 (20 MHz) transputer on the TRAM board. Each transputer in the modular system is a node of a ring network, whose root transputer node is hosted in a i386-based personal computer. After real-time data acquisition, a parallel reconstruction algorithm resolves time coincidences. Laboratory tests give a reconstruction time of 6.2 s for 1.28 10(5) events on 16 X + 16 Y channels (2 TDC + 2 TRAM), obtained in 1 s with a fluence of 5 X 10(4) events/mm2 (typically used in radiological imaging) on an area of 1.6 X 1.6 MM2

MODULAR DATA-ACQUISITION SYSTEM BASED ON TRANSPUTER TECHNOLOGY FOR BI-DIMENSIONAL TIME COINCIDENCE COUNTING

We describe the rationale and the test of a modular Data AcQuisition system (DAQ) for bi-dimensional (X-Y) digital imaging, based on a 16 channel Time-to-Digital Converter (TDC) NIM module connected to a specially designed TRAnsputer Module (TRAM). TDC time resolution is 12.5 ns (LSB) with a 40 MHz clock, time range is 3.3 s (28 bits), for a maximum rate of 500 kHz/channel guaranteed. The TDC + TRAM pair is the basic unit that can be scaled in modules of 8X + 8Y channels to meet the user's requirement for a larger number of X-Y channels to be considered simultaneously. TDC directly accesses the large RAM memory (32 Mbytes) of the INMOS T805 (20 MHz) transputer on the TRAM board. Each transputer in the modular system is a node of a ring network, whose root transputer node is hosted in a i386-based personal computer. After real-time data acquisition, a parallel reconstruction algorithm resolves time coincidences. Laboratory tests give a reconstruction time of 6.2 s for 1.28 10(5) events on 16 X + 16 Y channels (2 TDC + 2 TRAM), obtained in 1 s with a fluence of 5 X 10(4) events/mm2 (typically used in radiological imaging) on an area of 1.6 X 1.6 MM2

X-ray-imaging Test of A micro-strip Silicon Detector With A Transputer DAQ

We have developed a TDC+Transputer-based acquisition system to study the X-ray imaging capabilities of a silicon mustrip detector with 100 and 200 um read-out pitch. This system allows real-time image acquisition and display. We present images obtained with an X-ray mammography tube using sub-millimeter high contrast test objects on a 16x16 channels prototype