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Ion Traps and Quantum Computers (qCRs)

Amit Srivastava

Physicists at the NIST have built and tested a device for trapping electrically charged atoms (ions) that could process dozens of atoms at once. This design is an attempt to increase the numbers of ions trapped from few ions in a particular area to large trap arrays that can process many ions simultaneously in desired location.

The ion traps are device to trap single species; neutral or charged with the help of electro-magnetic fields. There are three types of trap widely used- Paul trap, Penning trap and a third their combination; Combined trap. The configuration of the Paul trap and Penning trap are the same; they both consist of a cylindrical, three electrode, symmetrical structure: two end-cap electrodes and a ring electrode.

In the Paul trap a combination of dc and radiofrequency voltages is applied to the electrodes. The equations of motion of an ion inside the Paul trap are Mathieu differential equations, which lead to both stable and unstable solutions depending on the operating parameters. By controlling these parameters, ions of a desired m/e range can be confined; other ions which are either intrinsically unstable or have large amplitudes collide with the trap electrodes and are lost. The Penning trap uses, as well as an axial magnetic field, an electric field with both end-cap at positive potential with respect to ring electrode. The effect of the electric field is to push the positive ions to the center and cause harmonic oscillations in the axial direction. The associated radial electric field, however, is repulsive and tends to push ions of the trap. It is the axial magnetic field which forces the ions into epicyclic trajectories resulting in their confinement. The ion-traps can be used to determination of the g-value of an electron from electron spin resonance experiments on a single electron, called the geonium atom, observation of quantum jumps in a single trapped ion, test of quantum Zeno effect, a precision test of linearity of quantum mechanics, a range of studies on one-component microplasmas, optical spectroscopy of molecular ions, precision mass measurement of radioactive isotopes, trapping and precision mass measurement of antiproton, lifetime measurement of neutron undergoing beta decay, atomic physics of highly charged ions etc.     

Made of a quartz wafer coated with gold in an oval shape roughly 2 by 4 millimeter, NIST’s “racetrack” features 150 work zones where quantum bits (qubit) ions encoding is 1s and 0s in their spin or other observable quantum properties- could be stored and transported using electrical fields and manipulated with laser beams for information processing. The trap’s higher version could store more quantum bits and use different materials.

Geometry is a key factor of the new design. This is the first example of ion transport through a junction in a trap where all electrodes are located on a single flat surface. This is marked improvement over a multilayer ion transport originally developed. The minimum number of adjacent electrodes required to hold an ion in an energy well are three.  This energy well and ion can be moved spatially though out the device applying voltage to other electrodes. The modular design would allow the addition of extra rings, which could significantly increase capabilities.

If they can be built qCR would rely on the rules of quantum mechanics to solve certain intractable problems, such as breaking today’s most widely used encryption codes. They can also be used for optimizing complex system such as airline schedule, much faster database searching and solving complex mathematical problems and even the development of novel products such as fraud proof digital signature. One of the most important consideration in qCRs is the fact that they scale polynomially rather than exponentially, as classical computers do. The polynomial scaling is what makes qCRs so useful for breaking encryption codes.      

The way ion-trap computing works require that ions be shuttled back and forth around the trap structure. The term “teleportation” is the word used to describe a transfer of “quantum states” between separate atoms. The technique may prove useful for transporting information in qCRs of the future, which could use the central processing elements smaller than an area of a sugar cube to carry out massively complex computations.

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