Selective coherence transfers in homonuclear dipolar coupled spin systems

Mapping the physical dipolar Hamiltonian of a solid-state network of nuclear spins onto a system of nearest-neighbor couplings would be extremely useful for a variety of quantum information processing applications, as well as NMR structural studies. We demonstrate such a mapping for a system consisting of an ensemble of spin pairs, where the coupling between spins in the same pair is significantly stronger than the coupling between spins on different pairs. An amplitude modulated RF field is applied on resonance with the Larmor frequency of the spins, with the frequency of the modulation matched to the frequency of the dipolar coupling of interest. The spin pairs appear isolated from each other in the regime where the RF power (omega_1) is such that omega_weak << omega_1 << omega_strong. Coherence lifetimes within the two-spin system are increased from 19 us to 11.1 ms, a factor of 572.Comment: 4 pages. Paper re-submitted with minor changes to clarify that the scheme demonstrated is not an exact mapping onto a nearest neighbor system. However, this is the first demonstration of a controlled evolution in a subspace of an extended spin system, on a timescale that is much larger than the dipolar dephasing tim

Effective Pure States for Bulk Quantum Computation

In bulk quantum computation one can manipulate a large number of indistinguishable quantum computers by parallel unitary operations and measure expectation values of certain observables with limited sensitivity. The initial state of each computer in the ensemble is known but not pure. Methods for obtaining effective pure input states by a series of manipulations have been described by Gershenfeld and Chuang (logical labeling) and Cory et al. (spatial averaging) for the case of quantum computation with nuclear magnetic resonance. We give a different technique called temporal averaging. This method is based on classical randomization, requires no ancilla qubits and can be implemented in nuclear magnetic resonance without using gradient fields. We introduce several temporal averaging algorithms suitable for both high temperature and low temperature bulk quantum computing and analyze the signal to noise behavior of each.Comment: 24 pages in LaTex, 14 figures, the paper is also avalaible at http://qso.lanl.gov/qc

Experimental Implementation of a Concatenated Quantum Error-Correcting Code

Concatenated coding provides a general strategy to achieve the desired level of noise protection in quantum information storage and transmission. We report the implementation of a concatenated quantum error-correcting code able to correct against phase errors with a strong correlated component. The experiment was performed using liquid-state nuclear magnetic resonance techniques on a four spin subsystem of labeled crotonic acid. Our results show that concatenation between active and passive quantum error-correcting codes offers a practical tool to handle realistic noise contributed by both independent and correlated errors.Comment: 4 pages, 2 encapsulated eps figures. REVTeX4 styl

Dynamics and Control of a Quasi-1D Spin System

We study experimentally a system comprised of linear chains of spin-1/2 nuclei that provides a test-bed for multi-body dynamics and quantum information processing. This system is a paradigm for a new class of quantum information devices that can perform particular tasks even without universal control of the whole quantum system. We investigate the extent of control achievable on the system with current experimental apparatus and methods to gain information on the system state, when full tomography is not possible and in any case highly inefficient

Separability of very noisy mixed states and implications for NMR quantum computing

We give a constructive proof that all mixed states of N qubits in a sufficiently small neighborhood of the maximally mixed state are separable. The construction provides an explicit representation of any such state as a mixture of product states. We give upper and lower bounds on the size of the neighborhood, which show that its extent decreases exponentially with the number of qubits. We also discuss the implications of the bounds for NMR quantum computing.Comment: 4 pages, extensively revised, references adde

Analisis Verifikasi Geometri Menggunakan EPID (Electronic Portal Imaging Device) Pada Penderita Kanker Cervix Yang Menjalani Terapi Radiasi Dengan Teknik 3DCRT Di Sub Instalasi Radioterapi RSUP Prof Dr. I. G. N. G Ngoerah

One of the cancers that causes the highest mortality is nasopharyngeal cancer. The number of nasopharyngeal cancer cases in Indonesia reached 19,943 new cases with a mortality rate of 13,399. Radiotherapy is the main treatment modality and part of standard care for cancer patients. The way radiotherapy works is to damage the DNA chain of tumor cells in order to kill tumor cells directly and eliminate the ability to proliferate. Giving radiation to the head and neck region has an influence on weight loss. The purpose of this study was to describe the BMI (Body Mass Index) of nasopharyngeal cancer patients who underwent IMRT therapy at the Radiotherapy Unit of Prof. Dr. I.G.N.G Ngoerah Hospital. The type of research used is quantitative research with an observational approach using retrospective data. The samples of this study were 25 patients with nasopharyngeal cancer who underwent IMRT therapy from January to December 2021 at the Radiotherapy Unit of Prof. Dr. I.G.N.G Ngoerah Hospital. The results of this study showed 25 samples of nasopharyngeal cancer patients who underwent IMRT therapy experienced weight loss with an average of 13.01 and BMI with an average of 4.93. Based on the results of the Statistical Test which shows that the p value &lt;0.05 which means there is a decrease in body weight in nasopharyngeal cancer patients undergoing IMRT therapy in the Radiotherapy Unit of Prof. Dr. I.G.N.G Ngoerah Hospital. Of the 25 samples of nasopharyngeal cancer patients who underwent IMRT therapy, there were changes in BMI (Body Mass Index) before irradiation and after irradiation. This is evident from the normality test value and Paired Twhich shows a p value &lt;0.05, meaning that there is a decrease in body weight in nasopharyngeal cancer patients undergoing IMRT therapy. &nbsp

Classical model for bulk-ensemble NMR quantum computation

We present a classical model for bulk-ensemble NMR quantum computation: the quantum state of the NMR sample is described by a probability distribution over the orientations of classical tops, and quantum gates are described by classical transition probabilities. All NMR quantum computing experiments performed so far with three quantum bits can be accounted for in this classical model. After a few entangling gates, the classical model suffers an exponential decrease of the measured signal, whereas there is no corresponding decrease in the quantum description. We suggest that for small numbers of quantum bits, the quantum nature of NMR quantum computation lies in the ability to avoid an exponential signal decrease.Comment: 14 pages, no figures, revte

Generation and detection of spin-orbit coupled neutron beams

Spin-orbit coupling of light has come to the fore in nano-optics and plasmonics, and is a key ingredient of topological photonics and chiral quantum optics. We demonstrate a basic tool for incorporating analogous effects into neutron optics: the generation and detection of neutron beams with coupled spin and orbital angular momentum. $^3$He neutron spin-filters are used in conjunction with specifically oriented triangular coils to prepare neutron beams with lattices of spin-orbit correlations, as demonstrated by their spin-dependant intensity profiles. These correlations can be tailored to particular applications, such as neutron studies of topological materials

Generating a Multipliciy of Policies for Agent Steering in Crowd Simulation

Pedestrian steering algorithms range from completely procedural to entirely data-driven, but the former grossly generalize across possible human behaviors and suffer computationally, whereas the latter are limited by the burden of ever-increasing data samples. Our approach seeks the balanced middle ground by deriving a collection of machine-learned policies based on the behavior of a procedural steering algorithm through the decomposition of the space of possible steering scenarios into steering contexts. The resulting algorithm scales well in the number of contexts, the use of new data sets to create new policies, and in the number of controlled agents as the policies become a simple evaluation of the rules asserted by the machine-learning process. We also explore the use of synthetic data from an “oracle algorithm” that serves as an as-needed source of samples, which can be stochastically polled for effective coverage. We observe that our approach produces pedestrian steering similar to that of the oracle steering algorithm, but with a significant performance boost. Runtime was reduced from hours under the oracle algorithm with 10 agents to on the order of 10 frames per second (FPS) with 3000 agents. We also analyze the nature of collisions in such a framework with no explicit collision avoidance