69 research outputs found
Scalable Emulation of Sign-ProblemFree Hamiltonians with Room Temperature p-bits
The growing field of quantum computing is based on the concept of a q-bit
which is a delicate superposition of 0 and 1, requiring cryogenic temperatures
for its physical realization along with challenging coherent coupling
techniques for entangling them. By contrast, a probabilistic bit or a p-bit is
a robust classical entity that fluctuates between 0 and 1, and can be
implemented at room temperature using present-day technology. Here, we show
that a probabilistic coprocessor built out of room temperature p-bits can be
used to accelerate simulations of a special class of quantum many-body systems
that are sign-problemfree or stoquastic, leveraging the well-known
Suzuki-Trotter decomposition that maps a -dimensional quantum many body
Hamiltonian to a +1-dimensional classical Hamiltonian. This mapping allows
an efficient emulation of a quantum system by classical computers and is
commonly used in software to perform Quantum Monte Carlo (QMC) algorithms. By
contrast, we show that a compact, embedded MTJ-based coprocessor can serve as a
highly efficient hardware-accelerator for such QMC algorithms providing several
orders of magnitude improvement in speed compared to optimized CPU
implementations. Using realistic device-level SPICE simulations we demonstrate
that the correct quantum correlations can be obtained using a classical
p-circuit built with existing technology and operating at room temperature. The
proposed coprocessor can serve as a tool to study stoquastic quantum many-body
systems, overcoming challenges associated with physical quantum annealers.Comment: Fixed minor typos and expanded Appendi
Autonomous Probabilistic Coprocessing with Petaflips per Second
In this paper we present a concrete design for a probabilistic (p-) computer
based on a network of p-bits, robust classical entities fluctuating between -1
and +1, with probabilities that are controlled through an input constructed
from the outputs of other p-bits. The architecture of this probabilistic
computer is similar to a stochastic neural network with the p-bit playing the
role of a binary stochastic neuron, but with one key difference: there is no
sequencer used to enforce an ordering of p-bit updates, as is typically
required. Instead, we explore \textit{sequencerless} designs where all p-bits
are allowed to flip autonomously and demonstrate that such designs can allow
ultrafast operation unconstrained by available clock speeds without
compromising the solution's fidelity. Based on experimental results from a
hardware benchmark of the autonomous design and benchmarked device models, we
project that a nanomagnetic implementation can scale to achieve petaflips per
second with millions of neurons. A key contribution of this paper is the focus
on a hardware metric flips per second as a problem and
substrate-independent figure-of-merit for an emerging class of hardware
annealers known as Ising Machines. Much like the shrinking feature sizes of
transistors that have continually driven Moore's Law, we believe that flips per
second can be continually improved in later technology generations of a wide
class of probabilistic, domain specific hardware.Comment: 13 pages, 8 figures, 1 tabl
Dynamic programming for finite ensembles of nanomagnetic particles
We use optimal control via a distributed exterior field to steer the dynamics of an ensemble of N interacting ferromagnetic particles which are immersed into a heat bath by minimizing a quadratic functional. Using the dynamic programming principle, we show the existence of a unique strong solution of the optimal control problem. By the Hopf–Cole transformation, the associated Hamilton–Jacobi–Bellman equation of the dynamic programming principle may be re-cast into a linear PDE on the manifold M=(S^2)^N, whose classical solution may be represented via Feynman–Kac formula. We use this probabilistic representation for Monte-Carlo simulations to illustrate optimal switching dynamics
Modeling of Nanoparticular Magnetoresistive Systems and the Impact on Molecular Recognition
Teich L, Kappe D, Rempel T, Meyer J, Schröder C, Hütten A. Modeling of Nanoparticular Magnetoresistive Systems and the Impact on Molecular Recognition. Sensors. 2015;15(4):9251-9264.The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or nanoparticles in conductive liquid gels and rearranging them by applying suitable external magnetic fields. After gelatinization of the gel matrix the bead or nanoparticle positions are fixed and the resulting system can be used as a magnetoresistive sensor. In order to optimize such sensor structures we have developed a simulation tool chain that allows us not only to study the structuring process in the liquid state but also to rigorously calculate the magnetoresistive characteristic curves for arbitrary nanoparticle arrangements. As an application, we discuss the role of magnetoresistive sensors in finding answers to molecular recognition
Quantum sensing
"Quantum sensing" describes the use of a quantum system, quantum properties
or quantum phenomena to perform a measurement of a physical quantity.
Historical examples of quantum sensors include magnetometers based on
superconducting quantum interference devices and atomic vapors, or atomic
clocks. More recently, quantum sensing has become a distinct and rapidly
growing branch of research within the area of quantum science and technology,
with the most common platforms being spin qubits, trapped ions and flux qubits.
The field is expected to provide new opportunities - especially with regard to
high sensitivity and precision - in applied physics and other areas of science.
In this review, we provide an introduction to the basic principles, methods and
concepts of quantum sensing from the viewpoint of the interested
experimentalist.Comment: 45 pages, 13 figures. Submitted to Rev. Mod. Phy
- …