Experimental Validation of Fully Quantum Fluctuation Theorems Using Dynamic Bayesian Networks.

Fluctuation theorems are fundamental extensions of the second law of thermodynamics for small systems. Their general validity arbitrarily far from equilibrium makes them invaluable in nonequilibrium physics. So far, experimental studies of quantum fluctuation relations do not account for quantum correlations and quantum coherence, two essential quantum properties. We here apply a novel dynamic Bayesian network approach to experimentally test detailed and integral fully quantum fluctuation theorems for heat exchange between two quantum-correlated thermal spins-1/2 in a nuclear magnetic resonance setup. We concretely verify individual integral fluctuation relations for quantum correlations and quantum coherence, as well as for the sum of all quantum contributions. We further investigate the thermodynamic cost of creating correlations and coherence.

Efficiency of a Quantum Otto Heat Engine Operating under a Reservoir at Effective Negative Temperatures.

We perform an experiment in which a quantum heat engine works under two reservoirs, one at a positive spin temperature and the other at an effective negative spin temperature, i.e., when the spin system presents population inversion. We show that the efficiency of this engine can be greater than that when both reservoirs are at positive temperatures. We also demonstrate the counterintuitive result that the Otto efficiency can be beaten only when the quantum engine is operating in the finite-time mode.

Reversing the direction of heat flow using quantum correlations.

Heat spontaneously flows from hot to cold in standard thermodynamics. However, the latter theory presupposes the absence of initial correlations between interacting systems. We here experimentally demonstrate the reversal of heat flow for two quantum correlated spins-1/2, initially prepared in local thermal states at different effective temperatures, employing a Nuclear Magnetic Resonance setup. We observe a spontaneous energy flow from the cold to the hot system. This process is enabled by a trade off between correlations and entropy that we quantify with information-theoretical quantities. These results highlight the subtle interplay of quantum mechanics, thermodynamics and information theory. They further provide a mechanism to control heat on the microscale.

Experimental Characterization of a Spin Quantum Heat Engine.

Developments in the thermodynamics of small quantum systems envisage nonclassical thermal machines. In this scenario, energy fluctuations play a relevant role in the description of irreversibility. We experimentally implement a quantum heat engine based on a spin-1/2 system and nuclear magnetic resonance techniques. Irreversibility at a microscope scale is fully characterized by the assessment of energy fluctuations associated with the work and heat flows. We also investigate the efficiency lag related to the entropy production at finite time. The implemented heat engine operates in a regime where both thermal and quantum fluctuations (associated with transitions among the instantaneous energy eigenstates) are relevant to its description. Performing a quantum Otto cycle at maximum power, the proof-of-concept quantum heat engine is able to reach an efficiency for work extraction (η≈42%) very close to its thermodynamic limit (η=44%).

Experimental Rectification of Entropy Production by Maxwell's Demon in a Quantum System.

Maxwell's demon explores the role of information in physical processes. Employing information about microscopic degrees of freedom, this "intelligent observer" is capable of compensating entropy production (or extracting work), apparently challenging the second law of thermodynamics. In a modern standpoint, it is regarded as a feedback control mechanism and the limits of thermodynamics are recast incorporating information-to-energy conversion. We derive a trade-off relation between information-theoretic quantities empowering the design of an efficient Maxwell's demon in a quantum system. The demon is experimentally implemented as a spin-1/2 quantum memory that acquires information, and employs it to control the dynamics of another spin-1/2 system, through a natural interaction. Noise and imperfections in this protocol are investigated by the assessment of its effectiveness. This realization provides experimental evidence that the irreversibility in a nonequilibrium dynamics can be mitigated by assessing microscopic information and applying a feed-forward strategy at the quantum scale.

Observation of Time-Invariant Coherence in a Nuclear Magnetic Resonance Quantum Simulator.

The ability to live in coherent superpositions is a signature trait of quantum systems and constitutes an irreplaceable resource for quantum-enhanced technologies. However, decoherence effects usually destroy quantum superpositions. It was recently predicted that, in a composite quantum system exposed to dephasing noise, quantum coherence in a transversal reference basis can stay protected for an indefinite time. This can occur for a class of quantum states independently of the measure used to quantify coherence, and it requires no control on the system during the dynamics. Here, such an invariant coherence phenomenon is observed experimentally in two different setups based on nuclear magnetic resonance at room temperature, realizing an effective quantum simulator of two- and four-qubit spin systems. Our study further reveals a novel interplay between coherence and various forms of correlations, and it highlights the natural resilience of quantum effects in complex systems.

High Resolution non-Markovianity in NMR.

Memoryless time evolutions are ubiquitous in nature but often correspond to a resolution-induced approximation, i.e. there are correlations in time whose effects are undetectable. Recent advances in the dynamical control of small quantum systems provide the ideal scenario to probe some of these effects. Here we experimentally demonstrate the precise induction of memory effects on the evolution of a quantum coin (qubit) by correlations engineered in its environment. In particular, we design a collisional model in Nuclear Magnetic Resonance (NMR) and precisely control the strength of the effects by changing the degree of correlation in the environment and its time of interaction with the qubit. We also show how these effects can be hidden by the limited resolution of the measurements performed on the qubit. The experiment reinforces NMR as a test bed for the study of open quantum systems and the simulation of their classical counterparts.

Experimental reconstruction of work distribution and study of fluctuation relations in a closed quantum system.

We report the experimental reconstruction of the nonequilibrium work probability distribution in a closed quantum system, and the study of the corresponding quantum fluctuation relations. The experiment uses a liquid-state nuclear magnetic resonance platform that offers full control on the preparation and dynamics of the system. Our endeavors enable the characterization of the out-of-equilibrium dynamics of a quantum spin from a finite-time thermodynamics viewpoint.

Protected quantum computing: interleaving gate operations with dynamical decoupling sequences.

Implementing precise operations on quantum systems is one of the biggest challenges for building quantum devices in a noisy environment. Dynamical decoupling attenuates the destructive effect of the environmental noise, but so far, it has been used primarily in the context of quantum memories. Here, we experimentally demonstrate a general scheme for combining dynamical decoupling with quantum logical gate operations using the example of an electron-spin qubit of a single nitrogen-vacancy center in diamond. We achieve process fidelities >98% for gate times that are 2 orders of magnitude longer than the unprotected dephasing time T2.

Presence of Salmonella spp. in reused broiler litter / Presencia de Salmonella spp. en cama reutilizada de pollos de engorde / Presença de Salmonella spp. em cama reutilizada de frangos de corte

Background: reutilization of poultry litter for multiple broiler flocks is a common practice in modern production systems due to the increasing scarcity and cost of bedding materials, and the necessity to reduce environmental impact. However, this practice has been associated with sanitary risks, such as the presence of Salmonella spp. in broiler meat. Objective: a study was conducted to detect the presence of Salmonella spp. in reused litters. Methods: 1,280 litter samples from Midwestern Brazilian poultry farms were analyzed during seven consecutive flocks. Samples were collected from flocks aged 28 to 32 days. Disposable shoe covers were used for sample collections. Presence of Salmonella spp. was determined by microbiological isolation. During the interval period between flocks the litter was fermented prior to its reuse by covering it with a black plastic canvas for 7 days. Results: positive samples for Salmonella spp. decreased when the number of litter reuses increased compared with the first reuse of the litter. An anaerobic digestion process with biological and physicochemical changes in the litter material and microbial communities may explain the low survival of pathogenic bacteria such as Salmonella spp. Conclusions: our study demonstrates that litter reused after the fermentation process is a safe and recommended practice to reduce the presence of Salmonella spp.

Antecedentes: la reutilización de la cama de pollos de engorde es una práctica común en el sistema moderno de producción avícola, sustentada por la reducción en el impacto ambiental, escasez de este material y disminución de costos de producción. Sin embargo, esta reutilización se ha asociado con riesgos sanitarios, tales como presencia de Salmonella spp. en los lotes de pollo. Objetivo: se realizó un estudio con el fin de detectar la presencia de Salmonella spp. en camas reutilizadas y fermentadas de pollos de engorde pertenecientes a granjas comerciales. Métodos: se analizaron 1280 muestras de cama de diversas granjas avícolas ubicadas en el centro oeste de Brasil durante siete lotes consecutivos de pollos. Las muestras de cama fueron tomadas de galpones con aves entre los 28 y 32 días de edad, utilizando polainas. La presencia de Salmonella spp. se determinó mediante aislamiento microbiológico. Durante el intervalo entre lotes, la cama fue fermentada antes de cada reutilización cubriendo la superficie entera de la cama con una lona de plástico negra por siete días. Resultados: fue observada una disminución en las muestras positivas para Salmonella con la reutilización y fermentación de las camas entre lotes, significativa con respecto al primer reuso. Esto indica que puede estar ocurriendo un proceso de digestión anaeróbica que conduce a que los procesos biológicos y físico-químicos entre el material de la cama y la comunidad microbiana allí presentes, estén afectando la supervivencia de bacterias patógenas como Salmonella. Conclusiones: nuestro estudio demuestra que la reutilización de la cama es una práctica segura y recomendable cuando se realiza después del proceso de fermentación, debido a que reduce la presencia de Salmonella spp.

Antecedentes: a reutilização de cama aviária por vários lotes é uma prática moderna do sistema de produção de aves, baseada na redução do impacto ambiental, escassez de este material e diminuição nos custos de produção. Porém, dita prática é associada com riscos sanitários como a presença de patógenos como Salmonella spp. nos lotes de frango. Objetivo: uma pesquisa foi realizada para detectar a presença de Salmonella spp. na cama reutilizada e fermentada de produtores de frango. Métodos: foram analisadas 1280 amostras de cama de diferentes produtores do Centro-oeste do Brasil durante sete lotes consecutivos. As amostras de cama foram coletadas com aves na idade entre 28 e 32 dias usando pró-pés descartáveis e a presença de Salmonella spp. foi determinada por isolamento bacteriológico. Durante o intervalo dos lotes a cama foi tratada antes da reutilização por meio da cobertura através de uma lona plástica preta em toda a superfície interna do aviário por sete dias. Resultados: foi observada uma diminuição no número de amostras positivas de Salmonella spp. com a reutilização e fermentação das camas entre os lotes, significativa em relação ao primeiro reuso. Isto indica que o processo de reutilização, seguido de fermentação anaeróbia do material da cama pela comunidade de microrganismos afetou a sobrevivência de bactérias patogênicas como Salmonella spp. Conclusões: este estudo evidencia que o reuso da cama é seguro e recomendado quando realizado após o processo de fermentação no intervalo do lote, devido a que diminui a presença de Salmonella spp.

Robust dynamical decoupling.

Quantum computers, which process information encoded in quantum mechanical systems, hold the potential to solve some of the hardest computational problems. A substantial obstacle for the further development of quantum computers is the fact that the lifetime of quantum information is usually too short to allow practical computation. A promising method for increasing the lifetime, known as dynamical decoupling (DD), consists of applying a periodic series of inversion pulses to the quantum bits. In the present review, we give an overview of this technique and compare different pulse sequences proposed earlier. We show that pulse imperfections, which are always present in experimental implementations, limit the performance of DD. The loss of coherence due to the accumulation of pulse errors can even exceed the perturbation from the environment. This effect can be largely eliminated by a judicious design of pulses and sequences. The corresponding sequences are largely immune to pulse imperfections and provide an increase of the coherence time of the system by several orders of magnitude.

Robust dynamical decoupling for quantum computing and quantum memory.

Dynamical decoupling (DD) is a popular technique for protecting qubits from the environment. However, unless special care is taken, experimental errors in the control pulses used in this technique can destroy the quantum information instead of preserving it. Here, we investigate techniques for making DD sequences robust against different types of experimental errors while retaining good decoupling efficiency in a fluctuating environment. We present experimental data from solid-state nuclear spin qubits and introduce a new DD sequence that is suitable for quantum computing and quantum memory.

Experimental magic state distillation for fault-tolerant quantum computing.

Any physical quantum device for quantum information processing (QIP) is subject to errors in implementation. In order to be reliable and efficient, quantum computers will need error-correcting or error-avoiding methods. Fault-tolerance achieved through quantum error correction will be an integral part of quantum computers. Of the many methods that have been discovered to implement it, a highly successful approach has been to use transversal gates and specific initial states. A critical element for its implementation is the availability of high-fidelity initial states, such as |0〉 and the 'magic state'. Here, we report an experiment, performed in a nuclear magnetic resonance (NMR) quantum processor, showing sufficient quantum control to improve the fidelity of imperfect initial magic states by distilling five of them into one with higher fidelity.