1,664 research outputs found
From the Quantum Approximate Optimization Algorithm to a Quantum Alternating Operator Ansatz
The next few years will be exciting as prototype universal quantum processors
emerge, enabling implementation of a wider variety of algorithms. Of particular
interest are quantum heuristics, which require experimentation on quantum
hardware for their evaluation, and which have the potential to significantly
expand the breadth of quantum computing applications. A leading candidate is
Farhi et al.'s Quantum Approximate Optimization Algorithm, which alternates
between applying a cost-function-based Hamiltonian and a mixing Hamiltonian.
Here, we extend this framework to allow alternation between more general
families of operators. The essence of this extension, the Quantum Alternating
Operator Ansatz, is the consideration of general parametrized families of
unitaries rather than only those corresponding to the time-evolution under a
fixed local Hamiltonian for a time specified by the parameter. This ansatz
supports the representation of a larger, and potentially more useful, set of
states than the original formulation, with potential long-term impact on a
broad array of application areas. For cases that call for mixing only within a
desired subspace, refocusing on unitaries rather than Hamiltonians enables more
efficiently implementable mixers than was possible in the original framework.
Such mixers are particularly useful for optimization problems with hard
constraints that must always be satisfied, defining a feasible subspace, and
soft constraints whose violation we wish to minimize. More efficient
implementation enables earlier experimental exploration of an alternating
operator approach to a wide variety of approximate optimization, exact
optimization, and sampling problems. Here, we introduce the Quantum Alternating
Operator Ansatz, lay out design criteria for mixing operators, detail mappings
for eight problems, and provide brief descriptions of mappings for diverse
problems.Comment: 51 pages, 2 figures. Revised to match journal pape
Charting the circuit QED design landscape using optimal control theory
With recent improvements in coherence times, superconducting transmon qubits
have become a promising platform for quantum computing. They can be flexibly
engineered over a wide range of parameters, but also require us to identify an
efficient operating regime. Using state-of-the-art quantum optimal control
techniques, we exhaustively explore the landscape for creation and removal of
entanglement over a wide range of design parameters. We identify an optimal
operating region outside of the usually considered strongly dispersive regime,
where multiple sources of entanglement interfere simultaneously, which we name
the quasi-dispersive straddling qutrits (QuaDiSQ) regime. At a chosen point in
this region, a universal gate set is realized by applying microwave fields for
gate durations of 50 ns, with errors approaching the limit of intrinsic
transmon coherence. Our systematic quantum optimal control approach is easily
adapted to explore the parameter landscape of other quantum technology
platforms.Comment: 13 pages, 5 figures, 2 pages supplementary, 1 supplementary figur
Several fitness functions and entanglement gates in quantum kernel generation
Quantum machine learning (QML) represents a promising frontier in the realm
of quantum technologies. In this pursuit of quantum advantage, the quantum
kernel method for support vector machine has emerged as a powerful approach.
Entanglement, a fundamental concept in quantum mechanics, assumes a central
role in quantum computing. In this paper, we study the necessities of
entanglement gates in the quantum kernel methods. We present several fitness
functions for a multi-objective genetic algorithm that simultaneously maximizes
classification accuracy while minimizing both the local and non-local gate
costs of the quantum feature map's circuit. We conduct comparisons with
classical classifiers to gain insights into the benefits of employing
entanglement gates. Surprisingly, our experiments reveal that the optimal
configuration of quantum circuits for the quantum kernel method incorporates a
proportional number of non-local gates for entanglement, contrary to previous
literature where non-local gates were largely suppressed.
Furthermore, we demonstrate that the separability indexes of data can be
effectively leveraged to determine the number of non-local gates required for
the quantum support vector machine's feature maps. This insight can
significantly aid in selecting appropriate parameters, such as the entanglement
parameter, in various quantum programming packages like https://qiskit.org/
based on data analysis. Our findings offer valuable guidance for enhancing the
efficiency and accuracy of quantum machine learning algorith
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