37 research outputs found
Quantum optimal control within the rotating wave approximation
We study the interplay between rotating wave approximation and optimal
control. In particular, we show that for a wide class of optimal control
problems one can choose the control field such that the Hamiltonian becomes
time-independent under the rotating wave approximation. Thus, we show how to
recast the functional minimization defined by the optimal control problem into
a simpler multi-variable function minimization. We provide the analytic
solution to the state-to-state transfer of the paradigmatic two-level system
and to the more general star configuration of an -level system. We
demonstrate numerically the usefulness of this approach in the more general
class of connected acyclic -level systems with random spectra. Finally, we
use it to design a protocol to entangle Rydberg via constant laser pulses atoms
in an experimentally relevant range of parameters.Comment: 8 pages, 5 figure
Entropy production and asymptotic factorization via thermalization: a collisional model approach
The Markovian evolution of an open quantum system is characterized by a
positive entropy production, while the global entropy gets redistributed
between the system and the environment degrees of freedom. Starting from these
premises, we analyze the entropy variation of an open quantum system in terms
of two distinct relations: the Clausius inequality, that provides an intrinsic
bound for the entropy variation in terms of the heat absorbed by the system,
and an extrinsic inequality, which instead relates the former to the
corresponding entropy increment of the environment. By modeling the
thermalization process with a Markovian collisional model, we compare and
discuss the two bounds, showing that the latter is asymptotically saturated in
the limit of large interaction time. In this regime not only the reduced
density matrix of the system reaches an equilibrium configuration, but it also
factorizes from the environment degrees of freedom. This last result is proven
analytically when the system-bath coupling is sufficiently strong and through
numerical analysis in the weak-coupling regime.Comment: 10 pages, 2 figure
Retention of Minority Students in a Bridge Program: Student Perceptions on Their Successes and Challenges
This study was an examination of the minority student retention rate in a year-long bridge program. The retention rate of these students is 25%. University administration was concerned about the retention rate and its impact on future enrollment. Using Jack Mezirow\u27s transformative learning as a framework of understanding, the purpose of this study was to identify successes and challenges that minority students experienced in the bridge program and how those experiences affected future decisions on retention. A qualitative case-study design was implemented and 9 of the 140 bridge students were purposefully selected for individual interviews. Data analysis was conducted using open coding procedures with iterative recategorization to identify the themes. Key findings indicated that students found peer mentoring, flexibility in lab schedules, and speakers to be successes. Challenges that students faced included efforts associated with self-regulation and self-efficacy. Based on these findings, a policy recommendation was developed for the local site that suggested developing a mentoring program and continued use of Student Support Services beyond the first year. The results of this study will help university administration make informed and strategic decisions to revise and enhance the bridge program towards a focus upon the improvement of minority student retention. Further, this study promotes social change by serving as a model for other institutions in similar situations and continues the conversation in the literature regarding minority student retention rate
Extractable work, the role of correlations, and asymptotic freedom in quantum batteries
We investigate a quantum battery made of N two-level systems, which is
charged by an optical mode via an energy-conserving interaction. We quantify
the fraction E(N) of energy stored in the B battery that can be extracted in
order to perform thermodynamic work. We first demonstrate that E(N) is highly
reduced by the presence of correlations between the charger and the battery or
B between the two-level systems composing the battery. We then show that the
correlation-induced suppression of extractable energy, however, can be
mitigated by preparing the charger in a coherent optical state. We conclude by
proving that the charger-battery system is asymptotically free of such locking
correlations in the N \to \infty limit.Comment: 5+4 page
Bladder cancer - the neglected tumor: a descriptive analysis of publications referenced in MEDLINE and data from the register clinicaltrials.gov
Background: Uro-oncological neoplasms have both a high incidence and mortality rate and are therefore a major public health problem. The aim of this study was to evaluate research activity in uro-oncology over the last decade.
Methods: We searched MEDLINE and ClinicalTrials.gov systematically for studies on prostatic, urinary bladder, kidney, and testicular neoplasms. The increase in newly published reports per year was analyzed using linear regression. The results are presented with 95% confidence intervals, and a p value <0.05 was considered statistically significant.
Results: The number of new publications per year increased significantly for prostatic, kidney and urinary bladder neoplasms (all <0.0001). We identified 1,885 randomized controlled trials (RCTs); also for RCTs, the number of newly published reports increased significantly for prostatic (p = 0.001) and kidney cancer (p = 0.005), but not for bladder (p = 0.09) or testicular (p = 0.44) neoplasms. We identified 3,114 registered uro-oncological studies in ClinicalTrials.gov. However, 85% of these studies are focusing on prostatic (45%) and kidney neoplasms (40%), whereas only 11% were registered for bladder cancers.
Conclusions: While the number of publications on uro-oncologic research rises yearly for prostatic and kidney neoplasms, urothelial carcinomas of the bladder seem to be neglected despite their important clinical role. Clinical research on neoplasms of the urothelial bladder must be explicitly addressed and supported
Chronotype is associated with psychological well-being depending on the composition of the study sample
Past studies examining the effect of chronotype and social jetlag on psychological well-being have been inconsistent so far. Here, we recruited participants from the general population and enquired about their natural sleeping behavior, sleep quality, depressive symptoms, and perceived stress. Partial correlations were computed between sleep variables and indicators of psychological well-being, controlling for age and sex. Less sleep during work days was found a good indicator for impairments in psychological well-being. In exploratory follow-up analyses, the same correlations were calculated within groups of early, intermediate, and late chronotype. We observed that the composition of the sample in terms of chronotype influenced whether associations between sleep variables and psychological well-being could be observed, a finding that is advised to be taken into account in future studies.Peer Reviewe
Dissipation in adiabatic quantum computers: lessons from an exactly solvable model
We introduce and study the adiabatic dynamics of free-fermion models subject to a local Lindblad bath and in the presence of a time-dependent Hamiltonian. The merit of these models is that they can be solved exactly, and will help us to study the interplay between nonadiabatic transitions and dissipation in many-body quantum systems. After the adiabatic evolution, we evaluate the excess energy (the average value of the Hamiltonian) as a measure of the deviation from reaching the final target ground state. We compute the excess energy in a variety of different situations, where the nature of the bath and the Hamiltonian is modified. We find robust evidence of the fact that an optimal working time for the quantum annealing protocol emerges as a result of the competition between the nonadiabatic effects and the dissipative processes. We compare these results with the matrix-product-operator simulations of an Ising system and show that the phenomenology we found also applies for this more realistic case
Outcomes and risks in palliative pancreatic surgery: an analysis of the German StuDoQ|Pancreas registry
BACKGROUND: Non-resectability is common in patients with pancreatic ductal adenocarcinoma (PDAC) due to local invasion or distant metastases. Then, biliary or gastroenteric bypasses or both are often established despite associated morbidity and mortality. The current study explores outcomes after palliative bypass surgery in patients with non-resectable PDAC. METHODS: From the prospectively maintained German StuDoQ|Pancreas registry, all patients with histopathologically confirmed PDAC who underwent non-resective pancreatic surgery between 2013 and 2018 were retrospectively identified, and the influence of the surgical procedure on morbidity and mortality was analyzed. RESULTS: Of 389 included patients, 127 (32.6%) underwent explorative surgery only, and a biliary, gastroenteric or double bypass was established in 92 (23.7%), 65 (16.7%) and 105 (27.0%). After exploration only, patients had a significantly shorter stay in the intensive care unit (mean 0.5 days [SD 1.7] vs. 1.9 [3.6], 2.0 [2.8] or 2.1 [2.8]; P < 0.0001) and in the hospital (median 7 days [IQR 4–11] vs. 12 [10–18], 12 [8–19] or 12 [9–17]; P < 0.0001), and complications occurred less frequently (22/127 [17.3%] vs. 37/92 [40.2%], 29/65 [44.6%] or 48/105 [45.7%]; P < 0.0001). In multivariable logistic regression, biliary stents were associated with less major (Clavien–Dindo grade ≥ IIIa) complications (OR 0.49 [95% CI 0.25–0.96], P = 0.037), whereas—compared to exploration only—biliary, gastroenteric, and double bypass were associated with more major complications (OR 3.58 [1.48–8.64], P = 0.005; 3.50 [1.39–8.81], P = 0.008; 4.96 [2.15–11.43], P < 0.001). CONCLUSIONS: In patients with non-resectable PDAC, biliary, gastroenteric or double bypass surgery is associated with relevant morbidity and mortality. Although surgical palliation is indicated if interventional alternatives are inapplicable, or life expectancy is high, less invasive options should be considered. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12893-022-01833-3
Many-body open quantum systems: from dynamics to thermodynamics
This thesis studies problems concerning the dynamics and thermodynamics of manybody
quantum systems. We start by introducing the necessary theoretical concepts and
tools forming the basis of this manuscript. The research presented can be split in two
parts. The first one deals with the dynamics of many-body quantum systems subject to
environmental dissipative effects of various forms, while the second one studies topics
of thermodynamics in many-body quantum systems.
The first part of the research presented studies the effects of an environment inducing
dissipation. We establish and study the adiabatic dynamics of free-fermion models
subject to a local Lindblad bath and in the presence of a time-dependent Hamiltonian.
The merit of these models is that they can be solved exactly, which thus can help us
to study the interplay between non-adiabatic transitions and dissipation in many-body
quantum systems. After the adiabatic evolution, we evaluate the excess energy (average
value of the Hamiltonian) as a measure of the deviation from reaching the target
final ground state. We find a robust evidence of the fact that an optimal working time
for the quantum annealing protocol emerges as a result of the competition between the
non-adiabatic effects and the dissipative processes. We compare these results with matrix
product operator simulations of an Ising system and show that the phenomenology
we found applies also for this more realistic case.
We then proceed to a scenario in which the environment is not detrimental, but is
on the contrary the driving force of the effects studied. We demonstrate that persistent
currents can be induced in a quantum system in contact with a structured reservoir,
without the need of any applied gauge field. The working principle of the mechanism
leading to their presence is based on the extension to the many-body scenario of
non-reciprocal Lindblad dynamics. Specifically, we consider an interacting spin/boson
model in a ring-shaped one-dimensional lattice coupled to an external bath. By employing
a combination of cluster mean-field, exact diagonalization and matrix product
operator techniques, we show that solely dissipative effects suffice to engineer steady
states with a persistent current that survives in the limit of large systems. We also
verify the robustness of such current in the presence of additional dissipative or Hamiltonian
perturbation terms.
The second part studies many-body quantum systems with a focus on thermodynamics.
First, we investigate a quantum battery made of N two-level systems, which
is charged by an optical mode via an energy-conserving interaction. We quantify the
fraction of energy stored in the battery that can be extracted in order to perform
thermodynamic work. We first demonstrate that this fraction is highly reduced by the presence of correlations between the charger and the battery or between the two-level
systems composing the battery. We then show that the correlation-induced suppression
of extractable energy, however, can be mitigated by preparing the charger in a
coherent optical state. We conclude by proving that the charger-battery system is
asymptotically free of such locking correlations in the N ! 1 limit.
And lastly, we study open questions within the theory of open quantum systems.
The Markovian evolution of an open quantum system is characterized by a positive
entropy production, while the global entropy gets redistributed between the system
and the environmental degrees of freedom. Starting from these premises, we analyse
the entropy variation of an open quantum system in terms of two distinct relations:
the Clausius inequality, that provides an intrinsic bound for the entropy variation in
terms of the heat absorbed by the system, and an extrinsic inequality, which instead
relates the former to the corresponding entropy increment of the environment. By
modeling the thermalization process with a Markovian collisional model, we compare
and discuss the two bounds, showing that the latter is asymptotically saturated in the
limit of large interaction time. In this regime not only the reduced density matrix
of the system reaches an equilibrium configuration, but it also factorizes from the
environmental degrees of freedom