Quantum metrology in the noisy intermediate-scale quantum era

Quantum metrology pursues the physical realization of higher-precision measurements to physical quantities than the classically achievable limit by exploiting quantum features, such as entanglement and squeezing, as resources. It has potential applications in developing next-generation frequency standards, magnetometers, radar, and navigation. However, the ubiquitous decoherence in the quantum world degrades the quantum resources and forces the precision back to or even worse than the classical limit, which is called the no-go theorem of noisy quantum metrology and greatly hinders its applications. Therefore, how to realize the promised performance of quantum metrology in realistic noisy situations attracts much attention in recent years. We will review the principle, categories, and applications of quantum metrology. Special attention will be paid to different quantum resources that can bring quantum superiority in enhancing sensitivity. Then, we will introduce the no-go theorem of noisy quantum metrology and its active control under different kinds of noise-induced decoherence situations.Comment: Minireview of quantum metrology based on Lectures given at the summer school "Fundamental and Frontiers of Quantum Metrology and Quantum Computation" held in Bohai University, China, from 23 July to 8 Augus

Quantum Control in Open and Periodically Driven Systems

Quantum technology resorts to efficient utilization of quantum resources to realize technique innovation. The systems are controlled such that their states follow the desired manners to realize different quantum protocols. However, the decoherence caused by the system-environment interactions causes the states deviating from the desired manners. How to protect quantum resources under the coexistence of active control and passive decoherence is of significance. Recent studies have revealed that the decoherence is determined by the feature of the system-environment energy spectrum: Accompanying the formation of bound states in the energy spectrum, the decoherence can be suppressed. It supplies a guideline to control decoherence. Such idea can be generalized to systems under periodic driving. By virtue of manipulating Floquet bound states in the quasienergy spectrum, coherent control via periodic driving dubbed as Floquet engineering has become a versatile tool not only in controlling decoherence, but also in artificially synthesizing exotic topological phases. We will review the progress on quantum control in open and periodically driven systems. Special attention will be paid to the distinguished role played by the bound states and their controllability via periodic driving in suppressing decoherence and generating novel topological phases.Comment: A review articl

Model Extraction Attack against Self-supervised Speech Models

Self-supervised learning (SSL) speech models generate meaningful representations of given clips and achieve incredible performance across various downstream tasks. Model extraction attack (MEA) often refers to an adversary stealing the functionality of the victim model with only query access. In this work, we study the MEA problem against SSL speech model with a small number of queries. We propose a two-stage framework to extract the model. In the first stage, SSL is conducted on the large-scale unlabeled corpus to pre-train a small speech model. Secondly, we actively sample a small portion of clips from the unlabeled corpus and query the target model with these clips to acquire their representations as labels for the small model's second-stage training. Experiment results show that our sampling methods can effectively extract the target model without knowing any information about its model architecture

Hydraulic fracturing propagation mechanism during shale gas reservoir stimulation through horizontal well

Način razlamanja stijenske mase u naslagama naftnih škriljaca jedan je od glavnih čimbenika koji djeluju na učinkovitost hidrauličkog frakturiranja (frakiranja). U ovom su radu provedena fizikalna ispitivanja i numeričko modeliranje u svrhu sustavnog ispitivanja učinka in-situ (podzemnog) naprezanja i kuta bušenja na stvaranje tlaka zbog hidrauličkog frakturiranja, širenje razlamanja i način razlamanja u horizontalnoj bušotini naftnog nalazišta Shengli u Luojia pokrajini, u izvođenju Sinopec Corp. Ukupno je razmatrano šest različitih in-situ kombinacija naprezanja i osam različitih kutova bušenja slojevite stijenske mase tijekom hidrauličkog frakturiranja. Sažetak nastanka i širenja pukotine te završni oblici pukotina nastalih hidrauličkim frakturiranjem u slojevitim stijenskim masama otkrivaju da kod stratificiranih stijena s istim kutom bušenja, što je veći in-situ omjer naprezanja (t.j. niže maksimalno horizontalno osnovno naprezanje pri konstantnim vertikalnim naprezanjem), potreban je niži hidraulički tlak za poticanje i širenje hidrauličkog frakturiranja. Štoviše, ustanovljeno je da je kod stratificirane stijenske mase pri istom omjeru naprezanja, tlak hidrauličkog frakturiranja, u slučaju kad je kut bušenja 30°, veći nego u svim drugim slučajevima. Nadalje, zapaženo je da učinak stratifikacije na hidrauličko frakturiranje postaje slabiji s porastom in-situ omjera naprezanja. Konačno je zaključeno da rezultati ove analize mogu biti važan teorijski pokazatelj u poboljšanju oblikovanja hidrauličkog frakturiranja kako bi se osiguralo učinkovito stimuliranje naslaga naftnih škriljaca.The fracture pattern of rock mass in shale gas reservoirs is one of the main factors affecting the efficiency of hydraulic fracturing. In this paper, physical experiments and numerical modelling were conducted to systematically investigate the effect of the in-situ stress and perforation angle on the hydraulic fracture initiation pressure and location, fracture propagation, and fracture pattern in a horizontal well drilled by Sinopec Corp. in Luojia area of Shengli Oilfield. A total of six different in-situ stress combinations and eight different perforation angles were considered for the stratified rock mass during the hydraulic fracturing. A summary of the fracture initiations and propagation, and the final fracture patterns induced by the hydraulic fracturing in the stratified rock masses reveals that, for the stratified rock masses with the same perforation angle, the larger the in-situ stress ratio (i.e. lower maximum horizontal principal stress when the vertical stress remains constant) is, the lower hydraulic pressure is required for hydraulic fracturing initiation and propagation. Moreover, it is found that, for the stratified rock mass under the same stress ratio, the hydraulic fracturing pressure in the case with a perforation angle of 30° is higher than that in all other cases. Furthermore, it is noted that the effect of the stratification on the hydraulic fracturing becomes weaker with the in-situ stress ratio increasing. It is finally concluded that the results from this study can provide important theoretical guidance for improving the hydraulic fracturing design in order to ensure the effective shale gas reservoir stimulations

Widespread occurrence of an emerging fungal pathogen in heavily traded Chinese urodelan species

Understanding introduction routes for wildlife pathogens is vital for the development of threat abatement plans. The chytrid fungus Batrachochytrium salamandrivorans (Bsal) has recently emerged in Europe, where it is considered to be a serious threat for urodelan conservation. If the highly diverse Chinese urodelans were to constitute a Bsal reservoir, then the significant international trade in these species may vector Bsal into naive urodelan communities. Here, we analyzed a total of 1,143 samples, representing 36 Chinese salamander species from 51 localities across southern China for the presence of Bsal. We found Bsal was present across a wide taxonomic, geographical, and environmental range. In particular, Bsal DNA was detected in 33 samples from the genera Cynops, Pachytriton, Paramesotriton, Tylototriton, and Andrias, including the heavily traded species Paramesotriton hongkongensis and Cynops orientalis. The true Bsal prevalence across our data set was estimated between 2% and 4%, with a maximum of 50% in a population of P. hongkongensis. Even at this overall relatively low Bsal prevalence, the exportation of millions of animals renders Bsal introduction in naive, importing countries a near certainty, which calls for the urgent implementation of proper biosecurity in the international wildlife trade