Magnetic Resonance Lithography with Nanometer Resolution

We propose an approach for super-resolution optical lithography which is based on the inverse of magnetic resonance imaging (MRI). The technique uses atomic coherence in an ensemble of spin systems whose final state population can be optically detected. In principle, our method is capable of producing arbitrary one and two dimensional high-resolution patterns with high contrast

A throughput optimal scheduling policy for a quantum switch

We study a quantum switch that creates shared end-to-end entangled quantum states to multiple sets of users that are connected to it. Each user is connected to the switch via an optical link across which bipartite Bell-state entangled states are generated in each time-slot with certain probabilities, and the switch merges entanglements of links to create end-to-end entanglements for users. One qubit of an entanglement of a link is stored at the switch and the other qubit of the entanglement is stored at the user corresponding to the link. Assuming that qubits of entanglements of links decipher after one time-slot, we characterize the capacity region, which is defined as the set of arrival rates of requests for end-to-end entanglements for which there exists a scheduling policy that stabilizes the switch. We propose a Max-Weight scheduling policy and show that it stabilizes the switch for all arrival rates that lie in the capacity region. We also provide numerical results to support our analysis

Coherent Population Trapping of Single Spins in Diamond Under Optical Excitation

Coherent population trapping is demonstrated in single nitrogen-vacancy centers in diamond under optical excitation. For sufficient excitation power, the fluorescence intensity drops almost to the background level when the laser modulation frequency matches the 2.88 GHz splitting of the ground states. The results are well described theoretically by a four-level model, allowing the relative transition strengths to be determined for individual centers. The results show that all-optical control of single spins is possible in diamond.Comment: minor correction

Optical and mechanical properties in photorefractive crystal based ultrasound-modulated optical tomography

Ultrasound-modulated optical tomography (UOT) is a new technique that combines laser light and ultrasound to provide images with good optical contrast and good ultrasound resolution in soft biological tissue. We improve the method proposed by Murray et al to obtain UOT images in thick biological tissues with the use of photorefractive crystal based interferometers. It is found that a long ultrasound burst (on the order of a millisecond) can improve the signal-to-noise ratio dramatically. Also with a long ultrasound burst, the response of the acoustic radiation force impulses can be clearly observed in the UOT signal, which will help to acquire images that record both the optical and mechanical properties of biological soft tissues

Ultrasound-modulated optical tomography using four-wave mixing in photorefractive polymers

Ultrasound-modulated optical tomography uses a well focused ultrasound beam to modulate diffuse light inside soft biological tissues. This modality combines the advantages of ultrasound resolution with optical contrast. However, because of the low ultrasound modulation efficiency, the large background of un-modulated photons gives a low signal-to-noise ratio. Here we report a technique for detection of ultrasound-modulated light using a phase conjugated signal generated by four-wave mixing in a photorefractive polymer. The experimental results demonstrate the potential of this method to detect ultrasound-modulated optical signals in a highly scattering media with an excellent signal-to-noise ratio

Sub-optical resolution of single spins using magnetic resonance imaging at room temperature in diamond

There has been much recent interest in extending the technique of magnetic resonance imaging (MRI) down to the level of single spins with sub-optical wavelength resolution. However, the signal to noise ratio for images of individual spins is usually low and this necessitates long acquisition times and low temperatures to achieve high resolution. An exception to this is the nitrogen-vacancy (NV) color center in diamond whose spin state can be detected optically at room temperature. Here we apply MRI to magnetically equivalent NV spins in order to resolve them with resolution well below the optical wavelength of the readout light. In addition, using a microwave version of MRI we achieved a resolution that is 1/270 size of the coplanar striplines, which define the effective wavelength of the microwaves that were used to excite the transition. This technique can eventually be extended to imaging of large numbers of NVs in a confocal spot and possibly to image nearby dark spins via their mutual magnetic interaction with the NV spin.Comment: 10 pages, 8 figures, Journal of Luminescence (Article in Press

Photorefractive detection of tissue optical and mechanical properties by ultrasound modulated optical tomography

Ultrasound-modulated optical tomography is a developing hybrid imaging modality that combines high optical contrast and good ultrasonic resolution for imaging soft biological tissue. We developed a photorefractive-crystal-based, time-resolved detection scheme with the use of a millisecond long ultrasound burst to image both the optical and the mechanical properties of biological tissues, with improved detection efficiency of ultrasound-tagged photons

Precise ultra fast single qubit control using optimal control pulses

Ultra fast and accurate quantum operations are required in many modern scientific areas - for instance quantum information, quantum metrology and magnetometry. However the accuracy is limited if the Rabi frequency is comparable with the transition frequency due to the breakdown of the rotating wave approximation (RWA). Here we report the experimental implementation of a method based on optimal control theory, which does not suffer these restrictions. We realised the most commonly used quantum gates - the Hadamard (\pi/2 pulse) and NOT (\pi pulse) gates with fidelities ($F^{\mathrm{exp}}_{\pi/2}=0.9472\pm0.01$ and $F^{\mathrm{exp}}_{\pi}=0.993\pm0.016$), in an excellent agreement with the theoretical predictions ($F^{\mathrm{theory}}_{\pi/2}=0.9545$ and $F^{\mathrm{theory}}_{\pi}=0.9986$). Moreover, we demonstrate magnetic resonance experiments both in the rotating and lab frames and we can deliberately "switch" between these two frames. Since our technique is general, it could find a wide application in magnetic resonance, quantum computing, quantum optics and broadband magnetometry.Comment: New, updated version of the manuscript with supplementary informatio