scholarly journals Quantum computing for classical problems: Variational Quantum Eigensolver for activated processes

2021 ◽  
Author(s):  
Pierpaolo Pravatto ◽  
Davide Castaldo ◽  
Federico Gallina ◽  
Barbara Fresch ◽  
Stefano Corni ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Nearest Neighbor ◽  
Stochastic Dynamics ◽  
Conformational Transition ◽  
Quantum Computer ◽  
Linear Chain ◽  
Thermal Fluctuations ◽  
Diffusive Regime ◽  
Error Mitigation ◽  
New Applications

Abstract The theory of stochastic processes impacts both physical and social sciences. At the molecular scale, stochastic dynamics is ubiquitous because of thermal fluctuations. The Fokker-Plank-Smoluchowski equation models the time evolution of the probability density of selected degrees of freedom in the diffusive regime and it is a workhorse of physical chemistry. In this paper, we report the development and implementation of a Variational Quantum Eigensolver procedure to solve the Fokker-Planck-Smoluchowski eigenvalue problem. We show that such an algorithm, typically adopted to address quantum chemistry problems, can be applied effectively to classical systems paving the way to new applications of quantum computers. We compute the conformational transition rate in a linear chain of rotors experiencing nearest-neighbor interaction. We provide a method to encode on the quantum computer the probability distribution for a given conformation of the chain and assess its scalability in terms of operations. Performance analysis on noisy quantum emulators and quantum devices (IBMQ Santiago) is provided for a small chain showing results in good agreement with the classical benchmark without further addition of any error mitigation technique.

scholarly journals Real-time simulation of (2+1)-dimensional lattice gauge theory on qubits

2020 ◽  
Author(s):  
Arata Yamamoto
Keyword(s):  
Gauge Theory ◽  
Real Time ◽  
Degrees Of Freedom ◽  
Quantum Computer ◽  
Lattice Gauge Theory ◽  
Dual Variable ◽  
Dimensional Lattice ◽  
The Real ◽  
Lattice Gauge ◽  
Time Simulation

Abstract We study the quantum simulation of Z2 lattice gauge theory in 2+1 dimensions. The dual variable formulation, the so-called Wegner duality, is utilized for reducing redundant gauge degrees of freedom. The problem of artificial charge unconservation is resolved for any charge distribution. As a demonstration, we simulate the real-time evolution of the system with two static electric charges, i.e., with two temporal Wilson lines. Some results obtained by the simulator (with no hardware noise) and the real device (with sizable hardware noise) of a quantum computer are shown.

ABSENCE OF PHASE TRANSITIONS ON TREE STRUCTURES

1993 ◽  
Vol 07 (29n30) ◽  
pp. 1947-1950 ◽  
Author(s):  
RAFFAELLA BURIONI ◽  
DAVIDE CASSI
Keyword(s):  
Long Range ◽  
Nearest Neighbor ◽  
Linear Chain ◽  
Mean Field ◽  
Range Order ◽  
The Other ◽  
Long Range Order ◽  
Field Phase ◽  
Tree Structures ◽  
Bethe Lattices

We rigorously prove that the correlation functions of any statistical model having a compact transitive symmetry group and nearest-neighbor interactions on any tree structure are equal to the corresponding ones on a linear chain. The exponential decay of the latter implies the absence of long-range order on any tree. On the other hand, for trees with exponential growth such as Bethe lattices, one can show the existence of a particular kind of mean field phase transition without long-range order.

scholarly journals Error mitigation with Clifford quantum-circuit data

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 592
Author(s):  
Piotr Czarnik ◽  
Andrew Arrasmith ◽  
Patrick J. Coles ◽  
Lukasz Cincio
Keyword(s):  
State Energy ◽  
Quantum Computer ◽  
Quantum Circuit ◽  
Training Data ◽  
Quantum Circuits ◽  
Accurate Estimation ◽  
Error Mitigation ◽  
Order Of Magnitude ◽  
Quantum Observables ◽  
Near Term

Achieving near-term quantum advantage will require accurate estimation of quantum observables despite significant hardware noise. For this purpose, we propose a novel, scalable error-mitigation method that applies to gate-based quantum computers. The method generates training data {Xinoisy,Xiexact} via quantum circuits composed largely of Clifford gates, which can be efficiently simulated classically, where Xinoisy and Xiexact are noisy and noiseless observables respectively. Fitting a linear ansatz to this data then allows for the prediction of noise-free observables for arbitrary circuits. We analyze the performance of our method versus the number of qubits, circuit depth, and number of non-Clifford gates. We obtain an order-of-magnitude error reduction for a ground-state energy problem on 16 qubits in an IBMQ quantum computer and on a 64-qubit noisy simulator.

scholarly journals Option Pricing using Quantum Computers

Quantum ◽  
2020 ◽  
Vol 4 ◽  
pp. 291 ◽  
Author(s):  
Nikitas Stamatopoulos ◽  
Daniel J. Egger ◽  
Yue Sun ◽  
Christa Zoufal ◽  
Raban Iten ◽  
...  
Keyword(s):  
Option Pricing ◽  
Quantum Computer ◽  
Quantum Circuits ◽  
Quantum Computers ◽  
Barrier Options ◽  
Error Mitigation ◽  
Quantum Device ◽  
Amplitude Estimation ◽  
Simulation Results ◽  
Path Dependent

We present a methodology to price options and portfolios of options on a gate-based quantum computer using amplitude estimation, an algorithm which provides a quadratic speedup compared to classical Monte Carlo methods. The options that we cover include vanilla options, multi-asset options and path-dependent options such as barrier options. We put an emphasis on the implementation of the quantum circuits required to build the input states and operators needed by amplitude estimation to price the different option types. Additionally, we show simulation results to highlight how the circuits that we implement price the different option contracts. Finally, we examine the performance of option pricing circuits on quantum hardware using the IBM Q Tokyo quantum device. We employ a simple, yet effective, error mitigation scheme that allows us to significantly reduce the errors arising from noisy two-qubit gates.

Fundamentals of Quantum Computing, Quantum Supremacy, and Quantum Machine Learning

2021 ◽  
pp. 21-46
Author(s):  
Kamaljit I. Lakhtaria ◽  
Vrunda Gadesha
Keyword(s):  
Machine Learning ◽  
Quantum Computing ◽  
Quantum Computer ◽  
Error Mitigation ◽  
Fundamental Goal ◽  
Quantum Device ◽  
Quantum Machine Learning ◽  
Simulation Error ◽  
The Difference ◽  
Quantum Optimization

When we aim to demonstrate that a programmable quantum device can solve complex problems which cannot be addressed by classic computers, this fundamental goal is known as quantum supremacy. This concept has changed every fundamental rule of computation. In this chapter, the detailed concept of quantum computing and quantum supremacy is explained along with various open source tools and real-time applications of this technology. The major base concepts, quantum computing, the difference between classical and quantum computer on physical level, programing quantum device, and the experiment-quantum supremacy are explained conceptually. This chapter also includes an introduction of the tools Cirq and OpenFermion plus the applications like quantum simulation, error mitigation technique, quantum machine learning, and quantum optimization, which are explained with illustrations.

The Debye theory of solid-state heat capacities

2021 ◽  
pp. 295-309
Author(s):  
Geoffrey Brooker
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Classical Limit ◽  
Degrees Of Freedom ◽  
Linear Chain ◽  
Heat Capacities ◽  
Debye Theory ◽  
State Heat ◽  
Equipartition Of Energy ◽  
Reasonable Step

“The Debye theory of solid-state heat capacities” gives a careful account of the Debye cut-off. We start by looking at a monatomic linear chain, leading to degrees of freedom and the equipartition of energy at the high-temperature (classical) limit. Reasonable approximations lead more naturally to the Born–von Karman model than to Debye, but Debye follows via a further reasonable step.

QUANTUM PHASE GATING WITH SEMICONDUCTOR QUANTUM DOTS IN A MICROCAVITY

2004 ◽  
Vol 18 (23) ◽  
pp. 1195-1203
Author(s):  
MANG FENG
Keyword(s):  
Quantum Dots ◽  
Degrees Of Freedom ◽  
Cavity Mode ◽  
Nearest Neighbor ◽  
Single Mode ◽  
Laser Pulses ◽  
Semiconductor Quantum Dots ◽  
Quantum Phase ◽  
Conduction Band Electron ◽  
Excitonic States

We propose a scheme to carry out quantum phase gate in one step by bichromatic radiation method with semiconductor quantum dots (QDs) embedded in a single mode microcavity. The spin degrees of freedom of the only excess conduction band electron are employed as qubits and excitonic states are used as auxiliary states. The nearest-neighbor coupling is not required because the cavity mode plays the role of data bus. We show how to perform quantum computing with properly tailored laser pulses and Pauli-blocking effect, without exciting the cavity mode.

Phase transitions in the adsorbed molecular chains

Open Physics ◽  
2005 ◽  
Vol 3 (1) ◽  
Author(s):  
Victor Lykah ◽  
Evgen Syrkin
Keyword(s):  
Effective Potential ◽  
Degrees Of Freedom ◽  
Nearest Neighbor ◽  
Structural Data ◽  
Dynamical Analysis ◽  
Second Phase ◽  
Integral Of Motion ◽  
Dynamical Equations ◽  
Nonlinear Dynamical ◽  
Wave Limit

AbstractRotational excitations of molecular adsorbed layers are studied theoretically. Nonlinear dynamical equations are obtained with accounting of quadrupolar interactions between molecules and freezing of translational degrees of freedom. The equilibrium positions of the molecules are found to be experimentally observed structures with alternating rotational ordering of planar rotors along the direction to the nearest neighbor (for linear or square structures) under low temperature. Dynamical analysis gives an integral of motion (energy) of the chain that in the long-wave limit leads consequently to the existence of four phases. The first one corresponds to oscillations near equilibrium ordered states. The second phase corresponds to low-energy rotational excitations along ‘valleys’ (easy directions in the effective potential) that do not destroy strong correlations between molecules while structural data can show rotational disorder (melting). The third phase corresponds to an energy that is enough to travel between ‘valleys’; only some ‘islands’ in the angle space are forbidden. Complete destruction of correlation when the energy is over the peaks of the effective potential corresponds to the fourth phase. Therefore rotational melting is a complex phenomenon that has several stages.

Magnetic Properties of the Random Mixture of the Classical Heisenberg Spins

1975 ◽  
Vol 53 (9) ◽  
pp. 854-860 ◽  
Author(s):  
Shigetoshi Katsura
Keyword(s):  
Critical Temperature ◽  
Nearest Neighbor ◽  
Linear Chain ◽  
Three Dimensional ◽  
Bethe Lattice ◽  
Zero Field ◽  
Qualitative Properties ◽  
Neighbor Interaction ◽  
Random Mixture ◽  
Ising Spins

The specific heat, the susceptibility, and the correlation function at zero field above the critical temperature of the random mixture (quenched site and bond problems) of the classical Heisenberg spins with nearest neighbor interaction were obtained exactly for the linear chain and for an infinite Bethe lattice (Bethe approximation of the two and three dimensional lattices) above the critical temperature. The results are simply expressed by the replacements of 2 cosh K → 4π (sinh K)/K and tanh K → L(K) (L(K) = Langevin function) for K = KAA, KAB, KBA, and KBB in the corresponding expressions of the random mixture of the Ising spins, and qualitative properties of both models are similar.

Sign in / Sign up

Export Citation Format

Share Document