New quantum technologies: batteries with qubits and electromagnetic resonators
Tesis

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2021Metadata
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Barra de la Guarda, Felipe
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New quantum technologies: batteries with qubits and electromagnetic resonators
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Abstract
In this thesis, an emerging quantum technology is studied as an open quantum system: the
quantum battery (QB). This new technology has recently emerged as a promising tool for
the thermodynamic control at the quantum scale [1 6]. A quantum battery is a quantum
mechanical system that behaves as an efficient energy storage device. Its realization is motivated
by the fact that genuine quantum effects such as entanglement or squeezing can
typically boost the performances of classical protocols, e.g., by speeding up the underlying
dynamics [7, 8]. These systems have been mostly studied neglecting the dissipation due to
the interaction with the environment surrounding them. In this thesis, the main focus is to
push forward the knowledge frontier in this regard, incorporating dissipation into the QB
system. In order to do so, numerical simulations were performed to study if the collective
effects that have been previously reported in QBs [9], still hold under dissipation. In particular,
the system studied is made out of N non-mutually interacting two-level systems (qubits)
charged via a single electromagnetic field mode in a resonator. This configuration is compared
to N copies of a resonator with one qubit. The former is a collective QB while the
latter is a parallel QB. The results show that the performance of parallel and collective QBs
(for instance, the power) decreases under dissipation as expected. Nevertheless, the ratio
between the power of the collective over the parallel QB increases with dissipation meaning
that the deterioration in performance is smaller for the collective QB. More remarkably, it is
found that the loss in performance due to dissipation can be reduced by scaling up the QB,
which means equally increasing the injected energy and number of qubits. In many systems
this is easier to do than decreasing dissipation. For example, nitrogen-vacancy centers in
diamond (NV centers), which can be prepared to behave as spin qubits, may be in groups of
hundreds in a sample of diamond [10]. This characteristic, together with its large values of
decoherence time (time before losing the quantum phase) and longitudinal relaxation time
(time before reaching thermal equilibrium) at room temperature [11], are the motivation to
analyze, in this thesis, the feasibility of making QBs with NV centers. As a result of this
analysis, it is concluded that for the type of QBs studied in this thesis, the technology is not
yet good enough to realize a so called charger-based QB. Nonetheless, a general experimental
restriction has been deduced, and the possibility of using NV centers for stable adiabatic QBs
(not the focus of this thesis) has been identified as promising future work. The collective
enhancements and performances were also studied in regard of charging energy, ergotropy
(maximum amount of extractable energy with unitary operations), and transfer rate. For
the first two, similar results as for the charging power are obtained. For the transfer rate,
instead, it is found that its collective enhancement decreases and its performance increases
as the dissipation rate increases. Last but not least, in the writing of this thesis, an effort to
introduce new common nomenclature in the area of QBs has been done, as the literature is
not completely consistent with the terms used up to now.
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Tesis para optar al grado de Magíster en Ciencias, Mención Física
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URI: https://repositorio.uchile.cl/handle/2250/184003
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