Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers1 and in searching a database2 by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system3, the superposition of single-particle quantum states is sufficient for Grover's algorithm4. Recently, the latter has been successfully implemented5 using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets6,7,8,9,10, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 105, with access times as short as 10-10 seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.

Quantum computing in molecular magnets

X-ray radiographic absorption imaging is an invaluable tool in medical diagnostics and materials science. For biological tissue samples, polymers or fibre composites, however, the use of conventional X-ray radiography is limited due to their weak absorption. This is resolved at highly brilliant X-ray synchrotron or micro-focus sources by using phase-sensitive imaging methods to improve the contrast1,2. However, the requirements of the illuminating radiation mean that hard-X-ray phase-sensitive imaging has until now been impractical with more readily available X-ray sources, such as X-ray tubes. In this letter, we report how a setup consisting of three transmission gratings can efficiently yield quantitative differential phase-contrast images with conventional X-ray tubes. In contrast with existing techniques, the method requires no spatial or temporal coherence, is mechanically robust, and can be scaled up to large fields of view. Our method provides all the benefits of contrast-enhanced phase-sensitive imaging, but is also fully compatible with conventional absorption radiography. It is applicable to X-ray medical imaging, industrial non-destructive testing, and to other low-brilliance radiation, such as neutrons or atoms.

http://xrm.phys.northwestern.edu/research/pdf_papers/2006/pfeiffer_naturephys_2006.pdf

Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources

If the fuel cell is to become the modern steam engine, basic research must provide breakthroughs in understanding, materials, and design to make a hydrogen-based energy system a vibrant and competitive force

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1878333

The Hydrogen Economy

Using a high-efficiency grating interferometer for hard X rays (10-30 keV) and a phase-stepping technique, separate radiographs of the phase and absorption profiles of bulk samples can be obtained from a single set of measurements. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index, with a spatial resolution down to a few microns. The method is mechanically robust, requires little spatial coherence and monochromaticity, and can be scaled up to large fields of view, with a detector of correspondingly moderate spatial resolution. These are important prerequisites for use with laboratory X-ray sources.

/pdf/x-ray-phase-imaging-with-a-grating-interferometer-4px897qwex.pdf

X-ray phase imaging with a grating interferometer.

The basic principles of x‐ray image formation and interpretation in radiography have remained essentially unchanged since Rontgen first discovered x rays over a hundred years ago. The conventional approach relies on x‐ray absorption as the sole source of contrast and draws exclusively on ray or geometrical optics to describe and interpret image formation. This approach ignores another, potentially more useful source of contrast—phase information. Phase‐sensitive techniques, which can be understood using wave optics rather than ray optics, offer ways to augment or complement standard absorption contrast by incorporating phase information.

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1292471

Phase‐Sensitive X‐Ray Imaging

Scientific collaboration networks

Blue and UV laser diodes can offer an efficient, stable alternative to LEDs for generating white light.

Lighting with laser diodes

Solid acids can have high proton conductivities. Recent experiments demonstrate that they may be sufficiently stable to form the core of new, higher efficiency fuel cells.

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1397388

Solid acids show potential for fuel cell electrolytes

Dreams of exploiting the spin of the electron in solid‐state devices underlie the nascent field of “spintronics.” Aspirations for semiconductors have been spurred by the development, in metals, of giant magneto‐resistance devices—as found in the read heads of current high‐density computer hard drives—and nonvolatile magnetic memory (see the PHYSICS TODAY special issue on magnetoelectronics, April 1995).

https://physicstoday.scitation.org/doi/pdf/10.1063/1.883032

Richard J. Fitzgerald

Papers

Phase‐Sensitive X‐Ray Imaging

Scientific collaboration networks

Lighting with laser diodes

Solid acids show potential for fuel cell electrolytes

Magnetic Semiconductors Enable Efficient Electrical Spin Injection