48 research outputs found
Variational neural network ansatz for steady states in open quantum systems
We present a general variational approach to determine the steady state of
open quantum lattice systems via a neural network approach. The steady-state
density matrix of the lattice system is constructed via a purified neural
network ansatz in an extended Hilbert space with ancillary degrees of freedom.
The variational minimization of cost functions associated to the master
equation can be performed using a Markov chain Monte Carlo sampling. As a first
application and proof-of-principle, we apply the method to the dissipative
quantum transverse Ising model.Comment: 6 pages, 4 figures, 54 references, 5 pages of Supplemental
Information
Variational dynamics of open quantum systems in phase space
We present a method to simulate the dynamics of large driven-dissipative
many-body open quantum systems using a variational encoding of the Wigner or
Husimi-Q quasi-probability distributions. The method relies on Monte-Carlo
sampling to maintain a polynomial computational complexity while allowing for
several quantities to be estimated efficiently. As a first application, we
present a proof of principle investigation into the physics of the
driven-dissipative Bose-Hubbard model with weak nonlinearity, providing
evidence for the high efficiency of the phase space variational approach.Comment: 7 pages, 5 figure
Embedding Classical Variational Methods in Quantum Circuits
We introduce a novel quantum-classical variational method that extends the
quantum devices capabilities to approximate ground states of interacting
quantum systems. The proposed method enhances parameterized quantum circuit
ansatzes implemented on quantum devices with classical variational functions,
such as neural-network quantum states. The quantum hardware is used as a
high-accuracy solver on the most correlated degrees of freedom, while the
remaining contributions are treated on a classical device. Our approach is
completely variational, providing a well-defined route to systematically
improve the accuracy by increasing the number of variational parameters, and
performs a global optimization of the two partitions at the same time. We
demonstrate the effectiveness of the protocol on spin chains and small
molecules and provide insights into its accuracy and computational cost. We
prove that our method is able to converge to exact diagonalization results via
the addition of classical degrees of freedom, while the quantum circuit is kept
fixed in both depth and width.Comment: 11 pages, 6 figure
An efficient quantum algorithm for the time evolution of parameterized circuits
We introduce a novel hybrid algorithm to simulate the real-time evolution of
quantum systems using parameterized quantum circuits. The method, named
"projected - Variational Quantum Dynamics" (p-VQD) realizes an iterative,
global projection of the exact time evolution onto the parameterized manifold.
In the small time-step limit, this is equivalent to the McLachlan's variational
principle. Our approach is efficient in the sense that it exhibits an optimal
linear scaling with the total number of variational parameters. Furthermore, it
is global in the sense that it uses the variational principle to optimize all
parameters at once. The global nature of our approach then significantly
extends the scope of existing efficient variational methods, that instead
typically rely on the iterative optimization of a restricted subset of
variational parameters. Through numerical experiments, we also show that our
approach is particularly advantageous over existing global optimization
algorithms based on the time-dependent variational principle that, due to a
demanding quadratic scaling with parameter numbers, are unsuitable for large
parameterized quantum circuits.Comment: 7+4 pages, 8 figures; Manuscript revised for publication. Method:
added Section 2.2, Results: added Figure 6, Appendix: added Appendix E with
Figure
Learning ground states of gapped quantum Hamiltonians with Kernel Methods
Neural network approaches to approximate the ground state of quantum
hamiltonians require the numerical solution of a highly nonlinear optimization
problem. We introduce a statistical learning approach that makes the
optimization trivial by using kernel methods. Our scheme is an approximate
realization of the power method, where supervised learning is used to learn the
next step of the power iteration. We show that the ground state properties of
arbitrary gapped quantum hamiltonians can be reached with polynomial resources
under the assumption that the supervised learning is efficient. Using kernel
ridge regression, we provide numerical evidence that the learning assumption is
verified by applying our scheme to find the ground states of several
prototypical interacting many-body quantum systems, both in one and two
dimensions, showing the flexibility of our approach
From Tensor Network Quantum States to Tensorial Recurrent Neural Networks
We show that any matrix product state (MPS) can be exactly represented by a
recurrent neural network (RNN) with a linear memory update. We generalize this
RNN architecture to 2D lattices using a multilinear memory update. It supports
perfect sampling and wave function evaluation in polynomial time, and can
represent an area law of entanglement entropy. Numerical evidence shows that it
can encode the wave function using a bond dimension lower by orders of
magnitude when compared to MPS, with an accuracy that can be systematically
improved by increasing the bond dimension.Comment: 14 pages, 10 figure
Unbiasing time-dependent Variational Monte Carlo by projected quantum evolution
We analyze the accuracy and sample complexity of variational Monte Carlo approaches to simulate the dynamics of many-body quantum systems classically. By systematically studying the relevant stochastic estimators, we are able to: (i) prove that the most used scheme, the time-dependent Variational Monte Carlo (tVMC), is affected by a systematic statistical bias or exponential sample complexity when the wave function contains some (possibly approximate) zeros, an important case for fermionic systems and quantum information protocols; (ii) show that a different scheme based on the solution of an optimization problem at each time step is free from such problems; (iii) improve the sample complexity of this latter approach by several orders of magnitude with respect to previous proofs of concept. Finally, we apply our advancements to study the high-entanglement phase in a protocol of non-Clifford unitary dynamics with local random measurements in 2D, first benchmarking on small spin lattices and then extending to large systems
Assessment of immunostimulatory responses to the antimiR-22 oligonucleotide compound RES-010 in human peripheral blood mononuclear cells
microRNA-22 (miR-22) is a key regulator of lipid and energy homeostasis and represents a promising therapeutic target for NAFLD and obesity. We have previously identified a locked nucleic acid (LNA)-modified antisense oligonucleotide compound complementary to miR-22, designated as RES-010 that mediated robust inhibition of miR-22 function in cultured cells and in vivo. In this study we investigated the immune potential of RES-010 in human peripheral blood mononuclear cells (PBMCs). We treated fresh human peripheral blood mononuclear cells isolated from six healthy volunteers with different concentrations of the RES-010 compound and assessed its proinflammatory effects by quantifying IL-1β, IL-6, IFN-γ, TNF-α, IFN-α2a, IFN-β, IL-10, and IL-17A in the supernatants collected 24 h of treatment with RES-010. The T-cell activation markers, CD69, HLA-DR, and CD25 were evaluated by flow cytometry after 24 and 144 h of treatment, respectively, whereas cell viability was assessed after 24 h of treatment with RES-010. Our results show that RES-010 compound does not induce any significant immunostimulatory responses in human PBMCs in vitro compared to controls, implying that the proinflammatory potential of RES-010 is low.</p