12 research outputs found
Availing non-Markovian dynamics in effective negative temperature-based transient quantum Otto engines
We demonstrate that the efficiency of effective negative temperature-based
quantum Otto engines, already known to outperform their traditional
counterparts operating with positive-temperature thermal reservoirs, can be
further improved by terminating the isochoric strokes before the working
substance reaches perfect equilibrium with its environment. Our investigation
encompasses both Markovian and non-Markovian dynamics during these finite-time
isochoric processes while considering a weak coupling between the working
substance and the reservoirs. We assess the performance of these engines as
they undergo a transition from the Markovian to the non-Markovian regime using
two figures of merit: maximum achievable efficiency at a certain finite time
during the isochoric heating stroke, and overall performance of the engine over
an extended period during the transient phase of this stroke. We show that the
maximum efficiency increases with the increase of non-Markovianity. However,
the overall engine performance decreases as non-Markovianity increases.
Additionally, we discover the existence of effective negative temperature-based
necessarily transient quantum Otto engines. These engines operate within an
extended operational domain, reaching into temperature ranges where
conventional effective negative temperature-based quantum Otto engines, which
rely on perfect thermalization or infinite-time protocols, are unable to
function. Furthermore, this extended operational domain of an effective
negative temperature-based necessarily transient quantum Otto engine increases
as non-Markovianity becomes more pronounced.Comment: 13 Pages, 4 Figure
Temperature- and interaction-tweaked efficiency boost of finite-time robust quantum Otto engines
We demonstrate that under specific conditions, a finite-time quantum Otto
engine, employing a spin-1/2 particle as the working substance, despite
undergoing incomplete Otto cycles, can achieve higher efficiency than an ideal
quantum Otto engine. A finite-time quantum Otto engine refers to an Otto engine
where the two isochoric strokes are prematurely terminated before reaching
thermal equilibrium with their respective hot and cold baths. We observe that
the enhancement of efficiency of a finite-time quantum Otto engine over the
ideal one can be realized by adjusting the initial temperature of the working
substance within the temperature range of the hot and cold baths. We also find
that incorporating an auxiliary qubit, and activating specific interactions
between the single-qubit working substance and the auxiliary one, can enhance
the efficiency of a finite-time as well as an ideal quantum Otto engine.
Furthermore, we analyze the impact of glassy disorder within the system-bath
coupling during the two isochoric strokes on the efficiency of a finite-time
quantum Otto engine. We find that as strength of disorder increases, efficiency
of a finite-time quantum Otto engine tends to decrease, albeit with relatively
modest reduction even for strong disorder. However, the advantage in efficiency
of the finite-time quantum Otto engine over the ideal one, obtained by tuning
the initial state temperature, and the efficiency enhancement obtained by
incorporating an auxiliary over the without-auxiliary scenario, persists even
in presence of substantial disorder. Additionally, we show that while this
disorder does not affect the ideal efficiency, it does influence the duration
of isochoric strokes needed for an Otto engine to reach ideal efficiency. This
stroke duration remains nearly constant until a specific disorder strength,
beyond which it increases rapidly.Comment: 14 pages, 7 figure
All multipartite entanglements are quantum coherences in locally distinguishable bases
We find that the m-separability and k-partite entanglement of a multipartite
quantum system is correlated with quantum coherence of the same with respect to
complete orthonormal bases, distinguishable under local operations and
classical communication in certain partitions. In particular, we show that the
geometric measure of m-inseparable entanglement of a multipartite quantum state
is equal to the square of minimum fidelity-based quantum coherence of the state
with respect to complete orthonormal bases, that are locally distinguishable in
a partition into m-parties.Comment: 8 page
Optimal quantum resource generation in coupled transmons immersed in Markovian baths
We analyze the quantum resource generation of capacitively-coupled multilevel
transmon circuits surrounded by bosonic baths, within the Markovian limit. In
practice, the superconducting circuit elements are usually part of a larger
circuit, constructed with many other linear circuit elements, which along with
their environment is assumed to be mimicked by the baths. We study the response
to variation of the coupling strength of resource generation for thee system
prepared in zero-resource initial states. We focus, in particular, on
entanglement and quantum coherence as resources. We quantify the entanglement
generation power of coupled transmon qutrits, taking into account the maximum
entanglement the system can generate and the time-scale over which the system
can sustain a significant entanglement. We identify the optimal initial
separable states leading to maximum entanglement generating power.Comment: comments are welcom
Estimating phase transition of perturbed J1-J2 Heisenberg quantum chain in mixtures of ground and first excited states
We show that the nearest neighbour entanglement in a mixture of ground and
first excited states - the subjacent state - of the J1-J2 Heisenberg quantum
spin chain can be used as an order parameter to detect the phase transition of
the chain from a gapless spin fluid to a gapped dimer phase. We study the
effectiveness of the order parameter for varying relative mixing probabilities
between the ground and first excited states in the subjacent state for
different system sizes, and extrapolate the results to the thermodynamic limit.
We observe that the nearest neighbour concurrence can play a role of a good
order parameter even if the system is in the ground state, but with a small
probability of leaking into the first excited state. Moreover, we apply the
order parameter of the subjacent state to investigate the response to
introduction of anisotropy and of glassy disorder on the phase diagram of the
model, and analyse the corresponding finite-size scale exponents and the
emergent tricritical point.Comment: 14 pages, 9 figure