scholarly journals Effective field theory during inflation: Reduced density matrix and its quantum master equation

2015 ◽  
Vol 92 (2) ◽  
Author(s):  
D. Boyanovsky
Keyword(s):  
Field Theory ◽  
Density Matrix ◽  
Master Equation ◽  
Effective Field Theory ◽  
Effective Field ◽  
Reduced Density Matrix ◽  
Quantum Master Equation ◽  
Reduced Density

scholarly journals An analysis of reading out the state of a charge quantum bit

2003 ◽  
Vol 3 (2) ◽  
pp. 121-138
Author(s):  
H-S. Goan
Keyword(s):  
Density Matrix ◽  
Master Equation ◽  
The State ◽  
Qubit State ◽  
Reduced Density Matrix ◽  
Quantum Trajectory ◽  
Single Shot ◽  
Quantum Bit ◽  
Trajectory Approach ◽  
Reduced Density

We provide a unified picture for the master equation approach and the quantum trajectory approach to a measurement problem of a two-state quantum system (a qubit), an electron coherently tunneling between two coupled quantum dots (CQD's) measured by a low transparency point contact (PC) detector. We show that the master equation of ``partially'' reduced density matrix can be derived from the quantum trajectory equation (stochastic master equation) by simply taking a ``partial'' average over the all possible outcomes of the measurement. If a full ensemble average is taken, the traditional (unconditional) master equation of reduced density matrix is then obtained. This unified picture, in terms of averaging over (tracing out) different amount of detection records (detector states), for these seemingly different approaches reported in the literature is particularly easy to understand using our formalism. To further demonstrate this connection, we analyze an important ensemble quantity for an initial qubit state readout experiment, P(N,t), the probability distribution of finding N electron that have tunneled through the PC barrier(s) in time t. The simulation results of P(N,t) using 10000 quantum trajectories and corresponding measurement records are, as expected, in very good agreement with those obtained from the Fourier analysis of the ``partially'' reduced density matrix. However, the quantum trajectory approach provides more information and more physical insights into the ensemble and time averaged quantity P(N,t). Each quantum trajectory resembles a single history of the qubit state in a single run of the continuous measurement experiment. We finally discuss, in this approach, the possibility of reading out the state of the qubit system in a single-shot experiment.

PATH INTEGRAL DERIVATION OF AN EXACT MASTER EQUATION

1995 ◽  
Vol 09 (02) ◽  
pp. 87-94 ◽  
Author(s):  
S. V. LAWANDE ◽  
Q. V. LAWANDE
Keyword(s):  
Density Matrix ◽  
Harmonic Oscillator ◽  
Master Equation ◽  
Path Integral ◽  
Open System ◽  
Coherent States ◽  
Reduced Density Matrix ◽  
Feynman Propagator ◽  
Reduced Density

The Feynman propagator in coherent states representation is obtained for a system of a single harmonic oscillator coupled to a reservoir of N oscillators. Using this propagator, an exact master equation is obtained for the evolution of the reduced density matrix for the open system of the oscillator.

scholarly journals Transverse momentum broadening of a jet in quark-gluon plasma: an open quantum system EFT

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Varun Vaidya ◽  
Xiaojun Yao
Keyword(s):  
Field Theory ◽  
Transverse Momentum ◽  
Master Equation ◽  
Effective Field Theory ◽  
Quark Gluon Plasma ◽  
Gluon Plasma ◽  
Effective Field ◽  
Jet Quenching ◽  
Jet Substructure ◽  
Open Quantum

Abstract We utilize the technology of open quantum systems in conjunction with the recently developed effective field theory for forward scattering to address the question of massless jet propagation through a weakly-coupled quark-gluon plasma in thermal equilibrium. We discuss various possible hierarchies of scales that may appear in this problem, by comparing thermal scales of the plasma with relevant scales in the effective field theory. Starting from the Lindblad equation, we derive and solve a master equation for the trans- verse momentum distribution of a massless quark jet, at leading orders both in the strong coupling and in the power counting of the effective field theory. Markovian approximation is justified in the weak coupling limit. Using the solution to the master equation, we study the transverse momentum broadening of a jet as a function of the plasma temperature and the time of propagation. We discuss the physical origin of infrared sensitivity that arises in the solution and a way to handle it in the effective field theory formulation. We suspect that the final measurement constraint can only cut-off leading infrared singularities and the solution to the Markovian master equation resums a logarithmic series. This work is a stepping stone towards understanding jet quenching and jet substructure observables on both light and heavy quark jets as probes of the quark-gluon plasma.

Effective Field Theory in Particle Physics and Cosmology

2020 ◽  
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
Particle Physics ◽  
Large Scale ◽  
Effective Field ◽  
Effective Theory ◽  
Soft Collinear Effective Theory ◽  
Multiple Length Scales ◽  
Cosmological Observations ◽  
Standard Models

Effective field theory (EFT) is a general method for describing quantum systems with multiple-length scales in a tractable fashion. It allows us to perform precise calculations in established models (such as the standard models of particle physics and cosmology), as well as to concisely parametrize possible effects from physics beyond the standard models. EFTs have become key tools in the theoretical analysis of particle physics experiments and cosmological observations, despite being absent from many textbooks. This volume aims to provide a comprehensive introduction to many of the EFTs in use today, and covers topics that include large-scale structure, WIMPs, dark matter, heavy quark effective theory, flavour physics, soft-collinear effective theory, and more.

The Fujita-Miyazawa force in the light of effective field theory

2008 ◽  
Author(s):  
Ulf-G. Meiβner ◽  
Hideyuki Sakai ◽  
Kimiko Sekiguchi ◽  
Benjamin F. Gibson
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
Effective Field

scholarly journals Towards Feynman rules for conformal blocks

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Sarah Hoback ◽  
Sarthak Parikh
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
Hypergeometric Functions ◽  
Power Series Expansion ◽  
Effective Field ◽  
Conformal Block ◽  
Tree Level ◽  
Conformal Blocks ◽  
Simple Set ◽  
Feynman Rules

Abstract We conjecture a simple set of “Feynman rules” for constructing n-point global conformal blocks in any channel in d spacetime dimensions, for external and exchanged scalar operators for arbitrary n and d. The vertex factors are given in terms of Lauricella hypergeometric functions of one, two or three variables, and the Feynman rules furnish an explicit power-series expansion in powers of cross-ratios. These rules are conjectured based on previously known results in the literature, which include four-, five- and six-point examples as well as the n-point comb channel blocks. We prove these rules for all previously known cases, as well as two new ones: the seven-point block in a new topology, and all even-point blocks in the “OPE channel.” The proof relies on holographic methods, notably the Feynman rules for Mellin amplitudes of tree-level AdS diagrams in a scalar effective field theory, and is easily applicable to any particular choice of a conformal block beyond those considered in this paper.

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