5,527 research outputs found
Technologies for trapped-ion quantum information systems
Scaling-up from prototype systems to dense arrays of ions on chip, or vast
networks of ions connected by photonic channels, will require developing
entirely new technologies that combine miniaturized ion trapping systems with
devices to capture, transmit and detect light, while refining how ions are
confined and controlled. Building a cohesive ion system from such diverse parts
involves many challenges, including navigating materials incompatibilities and
undesired coupling between elements. Here, we review our recent efforts to
create scalable ion systems incorporating unconventional materials such as
graphene and indium tin oxide, integrating devices like optical fibers and
mirrors, and exploring alternative ion loading and trapping techniques.Comment: 19 pages, 18 figure
A cryogenic surface-electrode elliptical ion trap for quantum simulation
Two-dimensional crystals of trapped ions are a promising system with which to
implement quantum simulations of challenging problems such as spin frustration.
Here, we present a design for a surface-electrode elliptical ion trap which
produces a 2-D ion crystal and is amenable to microfabrication, which would
enable higher simulated coupling rates, as well as interactions based on
magnetic forces generated by on-chip currents. Working in an 11 K cryogenic
environment, we experimentally verify to within 5% a numerical model of the
structure of ion crystals in the trap. We also explore the possibility of
implementing quantum simulation using magnetic forces, and calculate J-coupling
rates on the order of 10^3 / s for an ion crystal height of 10 microns, using a
current of 1 A
Prescription for experimental determination of the dynamics of a quantum black box
We give an explicit prescription for experimentally determining the evolution
operators which completely describe the dynamics of a quantum mechanical black
box -- an arbitrary open quantum system. We show necessary and sufficient
conditions for this to be possible, and illustrate the general theory by
considering specifically one and two quantum bit systems. These procedures may
be useful in the comparative evaluation of experimental quantum measurement,
communication, and computation systems.Comment: 6 pages, Revtex. Submitted to J. Mod. Op
Quantum Hypothesis Testing with Group Structure
The problem of discriminating between many quantum channels with certainty is
analyzed under the assumption of prior knowledge of algebraic relations among
possible channels. It is shown, by explicit construction of a novel family of
quantum algorithms, that when the set of possible channels faithfully
represents a finite subgroup of SU(2) (e.g., ) the
recently-developed techniques of quantum signal processing can be modified to
constitute subroutines for quantum hypothesis testing. These algorithms, for
group quantum hypothesis testing (G-QHT), intuitively encode discrete
properties of the channel set in SU(2) and improve query complexity at least
quadratically in , the size of the channel set and group, compared to
na\"ive repetition of binary hypothesis testing. Intriguingly, performance is
completely defined by explicit group homomorphisms; these in turn inform simple
constraints on polynomials embedded in unitary matrices. These constructions
demonstrate a flexible technique for mapping questions in quantum inference to
the well-understood subfields of functional approximation and discrete algebra.
Extensions to larger groups and noisy settings are discussed, as well as paths
by which improved protocols for quantum hypothesis testing against structured
channel sets have application in the transmission of reference frames, proofs
of security in quantum cryptography, and algorithms for property testing.Comment: 22 pages + 9 figures + 3 table
Multivariable quantum signal processing (M-QSP): prophecies of the two-headed oracle
Recent work shows that quantum signal processing (QSP) and its multi-qubit
lifted version, quantum singular value transformation (QSVT), unify and improve
the presentation of most quantum algorithms. QSP/QSVT characterize the ability,
by alternating ans\"atze, to obliviously transform the singular values of
subsystems of unitary matrices by polynomial functions; these algorithms are
numerically stable and analytically well-understood. That said, QSP/QSVT
require consistent access to a single oracle, saying nothing about computing
joint properties of two or more oracles; these can be far cheaper to determine
given an ability to pit oracles against one another coherently.
This work introduces a corresponding theory of QSP over multiple variables:
M-QSP. Surprisingly, despite the non-existence of the fundamental theorem of
algebra for multivariable polynomials, there exist necessary and sufficient
conditions under which a desired stable multivariable polynomial transformation
is possible. Moreover, the classical subroutines used by QSP protocols survive
in the multivariable setting for non-obvious reasons, and remain numerically
stable and efficient. Up to a well-defined conjecture, we give proof that the
family of achievable multivariable transforms is as loosely constrained as
could be expected. The unique ability of M-QSP to obliviously approximate joint
functions of multiple variables coherently leads to novel speedups
incommensurate with those of other quantum algorithms, and provides a bridge
from quantum algorithms to algebraic geometry.Comment: 23 pages + 4 figures + 10 page appendix (added background information
on algebraic geometry; publication in Quantum
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