7 research outputs found
Portable magnetometry for detection of biomagnetism in ambient environments
We present a method of optical magnetometry with parts-per-billion resolution
that is able to detect biomagnetic signals generated from the human brain and
heart in Earth's ambient environment. Our magnetically silent sensors measure
the total magnetic field by detecting the free-precession frequency of highly
spin-polarized alkali metal vapor. A first-order gradiometer is formed from two
magnetometers that are separated by a 3 cm baseline. Our gradiometer operates
from a laptop consuming 5 W over a USB port, enabled by state-of-the-art
micro-fabricated alkali vapor cells, advanced thermal insulation, custom
electronics, and laser packages within the sensor head. The gradiometer obtains
a sensitivity of 16 fT/cm/Hz outdoors, which we use to detect neuronal
electrical currents and magnetic cardiography signals. Recording of neuronal
magnetic fields is one of a few available methods for non-invasive functional
brain imaging that usually requires extensive magnetic shielding and other
infractructure. This work demonstrates the possibility of a dense array of
portable biomagnetic sensors that are deployable in a variety of natural
environments
Principles of an atomtronic transistor
A semiclassical formalism is used to investigate the transistor-like behavior
of ultracold atoms in a triple-well potential. Atom current flows from the
source well, held at fixed chemical potential and temperature, into an empty
drain well. In steady-state, the gate well located between the source and drain
is shown to acquire a well-defined chemical potential and temperature, which
are controlled by the relative height of the barriers separating the three
wells. It is shown that the gate chemical potential can exceed that of the
source and have a lower temperature. In electronics terminology, the
source-gate junction can be reverse-biased. As a result, the device exhibits
regimes of negative resistance and transresistance, indicating the presence of
gain. Given an external current input to the gate, transistor-like behavior is
characterized both in terms of the current gain, which can be greater than
unity, and the power output of the device.Comment: 15 pages, 5 figures, accepted for publication in NJ