Vishal Shah
University of Colorado Boulder
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Publication
Featured researches published by Vishal Shah.
Applied Physics Letters | 2004
Svenja Knappe; Vishal Shah; Peter D. D. Schwindt; Leo W. Hollberg; John Kitching; Li-Anne Liew; John M. Moreland
Fabrication techniques usually applied to microelectromechanical systems (MEMS) are used to reduce the size and operating power of the core physics assembly of an atomic clock. With a volume of 9.5mm3, a fractional frequency instability of 2.5×10−10 at 1s of integration, and dissipating less than 75mW of power, the device has the potential to bring atomically precise timing to hand-held, battery-operated devices. In addition, the design and fabrication process allows for wafer-level assembly of the structures, enabling low-cost mass-production of thousands of identical units with the same process sequence, and easy integration with other electronics.
Optics Letters | 2005
Svenja Knappe; Vladislav Gerginov; Peter D. D. Schwindt; Vishal Shah; Hugh Robinson; Leo W. Hollberg; John Kitching
A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.
Optics Express | 2005
Svenja Knappe; Peter D. D. Schwindt; Vishal Shah; Leo W. Hollberg; John Kitching; Li-Anne Liew; John M. Moreland
We demonstrate a microfabricated atomic clock physics package based on coherent population trapping (CPT) on the D1 line of 87Rb atoms. The package occupies a volume of 12 mm3 and requires 195 mW of power to operate at an ambient temperature of 200 degrees C. Compared to a previous microfabricated clock exciting the D2 transition in Cs [1], this 87Rb clock shows significantly improved short- and long-term stability. The instability at short times is 4 x?10-11 / tau?/2 and the improvement over the Cs device is due mainly to an increase in resonance amplitude. At longer times (tau?> 50 s), the improvement results from the reduction of a slow drift to ?5 x 10-9 / day. The drift is most likely caused by a chemical reaction of nitrogen and barium inside the cell. When probing the atoms on the D1 line, spin-exchange collisions between Rb atoms and optical pumping appear to have increased importance compared to the D2 line.
Applied Physics Letters | 2007
Peter D. D. Schwindt; Brad Lindseth; Svenja Knappe; Vishal Shah; John Kitching; Li-Anne Liew
The fabrication and performance of a miniature optically pumped atomic magnetometer constructed with microfabricated components are discussed. This device measures the spin precession frequency of Rb87 atoms to determine the magnetic field by use of the Mx technique. It has a demonstrated sensitivity to magnetic fields of 5pT∕Hz1∕2 for a bandwidth from 1to100Hz, nearly an order of magnitude improvement over our previous chip-scale magnetometer. The 3dB bandwidth has also been increased to 1kHz by reconfiguring the miniature vapor cell heater.
Proceedings of the National Academy of Sciences of the United States of America | 2008
Micah P. Ledbetter; Igor Savukov; Dmitry Budker; Vishal Shah; Svenja Knappe; John Kitching; David Michalak; Shoujun Xu; Alexander Pines
We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sample by eliminating the need for a solenoid to create a leading field. We achieve pulsed NMR linewidths of 26 Hz, limited, we believe, by the residence time and flow dispersion in the encoding region. In a fully optimized system, we estimate that for 1 s of integration, 7 × 1013 protons in a volume of 1 mm3, prepolarized in a 10-kG field, can be detected with a signal-to-noise ratio of ≈3. This level of sensitivity is competitive with that demonstrated by microcoils in 100-kG magnetic fields, without requiring superconducting magnets.
NeuroImage | 2017
Elena Boto; Sofie S. Meyer; Vishal Shah; Orang Alem; Svenja Knappe; Peter Krüger; T. Mark Fromhold; Mark Lim; Paul Glover; Peter G. Morris; Richard Bowtell; Gareth R. Barnes; Matthew J. Brookes
ABSTRACT Advances in the field of quantum sensing mean that magnetic field sensors, operating at room temperature, are now able to achieve sensitivity similar to that of cryogenically cooled devices (SQUIDs). This means that room temperature magnetoencephalography (MEG), with a greatly increased flexibility of sensor placement can now be considered. Further, these new sensors can be placed directly on the scalp surface giving, theoretically, a large increase in the magnitude of the measured signal. Here, we present recordings made using a single optically‐pumped magnetometer (OPM) in combination with a 3D‐printed head‐cast designed to accurately locate and orient the sensor relative to brain anatomy. Since our OPM is configured as a magnetometer it is highly sensitive to environmental interference. However, we show that this problem can be ameliorated via the use of simultaneous reference sensor recordings. Using median nerve stimulation, we show that the OPM can detect both evoked (phase‐locked) and induced (non‐phase‐locked oscillatory) changes when placed over sensory cortex, with signals ˜4 times larger than equivalent SQUID measurements. Using source modelling, we show that our system allows localisation of the evoked response to somatosensory cortex. Further, source‐space modelling shows that, with 13 sequential OPM measurements, source‐space signal‐to‐noise ratio (SNR) is comparable to that from a 271‐channel SQUID system. Our results highlight the opportunity presented by OPMs to generate uncooled, potentially low‐cost, high SNR MEG systems.
Advances in Atomic Molecular and Optical Physics | 2010
Vishal Shah; John Kitching
Abstract We review advances in the field of coherent population trapping (CPT) over the last decade with respect to the application of this physical phenomenon to atomic frequency references. We provide an overview of both the basic phenomenon of CPT and how it has traditionally been used in atomic clocks. We then describe a number of advances made with the goal of improving the resonance contrast, decreasing its line width, and reducing light shifts that affect the long-term stability. We conclude with a discussion of how these new approaches can impact future generations of laboratory and commercial instruments.
Metrologia | 2005
John Kitching; Svenja Knappe; Li-Anne Liew; John M. Moreland; Peter D. D. Schwindt; Vishal Shah; Vladislav Gerginov; Leo W. Hollberg
Using microfabrication processes, we have been able to construct physics packages for vapour cell atomic frequency references 100× smaller than previously existing versions, with a corresponding reduction in power consumption. In addition, the devices offer the potential for wafer-level fabrication and assembly, which would substantially reduce manufacturing costs. It is anticipated that a complete frequency reference could be constructed based on these physics packages with a total volume below 1 cm3, a power dissipation near 30 mW and a fractional frequency instability below 10−11 over time periods from hours to days. Such a device would enable the use of atomically precise timing in applications that require battery operation and portability, such as hand-held global positioning system receivers and wireless communication systems.
Optics Express | 2006
M. Rosenbluh; Vishal Shah; Svenja A. Knappe; John Kitching
We demonstrate the excitation and low-noise differential detection of a coherent population trapping (CPT) resonance with two modulated optical fields with orthogonal circular polarizations. When a microwave phase delay of lambda/4 is introduced in the optical path of one of the fields, the difference in the power transmitted through the cell in each polarization shows a narrow, dispersive resonance. The differential detection allows a high degree of suppression of laser-induced noise and will enable nearly shot-noise-limited operation of atomic frequency references and magnetometers based on CPT.
Journal of The Optical Society of America B-optical Physics | 2006
Vladislav Gerginov; Svenja A. Knappe; Vishal Shah; Peter D. D. Schwindt; Leo W. Hollberg; John Kitching
We present an evaluation of the long-term frequency instability and environmental sensitivity of a chip-scale atomic clock based on coherent population trapping, particularly as affected by the light-source subassembly. The long-term frequency stability of this type of device can be dramatically improved by judicious choice of operating parameters of the light-source subassembly. We find that the clock frequency is influenced by the laser-injection current, the laser temperature, and the rf modulation index. The sensitivity of the clock frequency to changes in the laser-injection current or the substrate temperature can be significantly reduced through adjustment of the rf modulation index. This makes the requirements imposed on the laser-temperature stabilization, in order to achieve a given frequency stability, less severe. The clock-frequency instability due to variations in local oscillator power is shown to be reduced through the choice of an appropriate light intensity inside the cell. The importance of these parameters with regard to the long-term stability of such systems is discussed.