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October 09, 2009

Atomtronic Circuits of Diodes and Transistors

Atomtronics has the goal of developing a one-to-one analogy of electronic systems, components and devices with ultracold atoms trapped in optical lattices It is being researched at the University of Colorado. The Atomtronic Anderson Group of Optical Physics

Their atom-optical analogy to electronic circuits begins with the definition of the `atomtronic battery', which is composed of two reservoirs of ultracold atoms having different chemical potentials (corresponding to different electric potentials at the terminals of a conventional battery). The `wires' and atomtronic components are composed of optical lattices, and current refers to the number of atoms that pass a specific point in a given amount of time.

Atomtronic Diode
The atomtronic diode is a device that allows an atomic flux to flow across it in essentially only one direction. It is made by adding a potential step, which emulates a semiconductor junction (the boundary between p-type and n-type solid-state materials), to an energetically-flat optical lattice


Atomtronic analogy to a simple diode circuit. The atomtronic analogy of a diode formed from the joining of p-type and n-type semiconductor materials. Electrons are replaced by ultracold atoms, the battery is replaced by high and low chemical potential reservoirs, and the metallic crystal lattices (the microscopic medium that the electrons traverse) are replaced by an optical lattice. The atomtronic diode is achieved by energetically shifting one half of the optical lattice with respect to the other.



The atomtronic transistor
The desired function of an atomtronic transistor is to enable a weak atomtronic current to be amplified or to switch,either on or off, a much larger one. Transistor action requires at least three lattice sites connected to three independent reservoirs. The resonance condition for this device is found to be an extension of the diode case to account for the third well: the left external energy is shifted above the middle site by the on-site interaction energy and is of equal energy to that of the right site.


Dynamics of the atomtronic transistor.(a) A cartoon of the atomtronic transistor as a three-well system, where each well is connected to its own independent reservoir. (b) An energy schematic of the relevant states of the system under the assumed resonance condition. In both illustrated cases, there is a fixed chemical potential difference across the system. In case 1, the middle chemical potential maintains an occupancy of zero particles on the middle site and most of the population remains on the left site. In case 2, the base potential is raised to put one particle on the middle site. This triggers two competing cycles that, given weak coupling of the middle reservoir, causes an avalanche of current to flow across the system. (c) An exact calculation of the current responses of the atomtronic transistor. The middle reservoir here has one-tenth the coupling strength of the left and right reservoirs. For a fixed chemical potential difference across the device, we vary the middle potential and record the response of currents leaving the system from both the right site (blue) as well as out of the middle site (red). The differential current gain for this specific system is both large and essentially linear
Atomtronic Circuits of Diodes and Transistors in Physic Review Letters

From Physorg: Atomtronics probably won’t replace electronics. “Atoms are sluggish compared to electrons, and that means that you probably won’t see atomtronics replace current electronic devices. What atomtronics might be useful for is the field of quantum information.”

The dynamics of our atomtronic devices would be coherent and potentially useful in quantum computing.” He also suggests that there is the possibility that atomtronics could be useful in obtaining sensitive measurements. At the very least, he concludes, “atomtronic systems provide a nice test of fundamental concepts in condensed matter physics.”

While these ideas have been modeled, they have yet to be built. Pepino says that an effort is under way to set up experiments that could provide a proof of principle for the work being done at JILA and the University of Colorado by experimantal collaborator and co-author Dana Anderson.


We illustrate that open quantum systems composed of neutral, ultracold atoms in one-dimensional optical lattices can exhibit behavior analogous to semiconductor electronic circuits. A correspondence is demonstrated for bosonic atoms, and the experimental requirements to realize these devices are established. The analysis follows from a derivation of a quantum master equation for this general class of open quantum systems.



Atomtronics: Ultracold-atom analogs of electronic devices (from 2007)

Atomtronics focuses on atom analogs of electronic materials, devices, and circuits. A strongly interacting ultracold Bose gas in a lattice potential is analogous to electrons in solid-state crystalline media. As a consequence of the gapped many-body energy spectrum, cold atoms in a lattice exhibit insulatorlike or conductorlike properties. P-type and N-type material analogs are created by introducing impurity sites into the lattice. Current through an atomtronic wire is generated by connecting the wire to an atomtronic battery which maintains the two contacts at different chemical potentials. The design of an atomtronic diode with a strongly asymmetric current-voltage curve exploits the existence of superfluid and insulating regimes in the phase diagram. The atom analog of a bipolar junction transistor exhibits large negative gain. Our results provide the building blocks for more advanced atomtronic devices and circuits such as amplifiers, oscillators, and fundamental logic gates.


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