Tiny electrical charges may advance the development of quantum computers
Since the electric charge of the electron was measured for the first time, about 80 years ago, by the American physicist Robert Millikan, this charge is considered the basic, smallest unit of electric charge. But since then, theories have been developed regarding the existence of simulated particles carrying smaller electric charges, which were indeed measured in experiments performed by Prof. Motty Highblom and members of his research group in the Department of Condensed Matter Physics at the Weizmann Institute of Science. But recently it became clear that there are actually different types of simulated particles that carry electric charges that are smaller than the charge of the electron. These findings may be of great importance in the way of developing quantum computers.
One theory regarding electric charges smaller than the charge of the electron was proposed in 1982 by the American physicist Robert Leflin as part of an explanation of certain electronic phenomena. From Leflin's explanation, it was assumed that under certain conditions a kind of structures of electrons are formed in the electric current that function as "simulated particles", each of which carries an electrical charge smaller than the "basic" charge of a single electron (a third of the electron's charge, a fifth of it, a seventh of it, and even smaller parts). The first proof of the correctness of Leflin's theory was provided by the members of Prof. Hyblum's research group. They were able to measure, for the first time in the world, the electric charges of "simulated particles", which were indeed equal to a third and a fifth of the charge of a single electron. This proof played an important role in the decision to award the 1998 Nobel Prize in Physics to Robert Leflin, Horst Sturmer and Daniel Tsoi.
Leflin's theory, which explains certain quantum phenomena, predicts the existence of simulated particles carrying a charge that is a fraction of the electron's charge, and more precisely, a fraction with an odd denominator (one-third, one-fifth, one-seventh). But experiments examining other quantum phenomena indicated the possibility of the existence of simulated particles of a completely different type: ones whose electric charge would be equal to a quarter of the charge of the electron. Prof. Highblom and the members of his research group recently proved the existence of these simulated particles, and were able to measure their electric charge, which is equal to a quarter of the charge of the electron. The experiment was made possible, among other things, thanks to the fact that Dr. Vladimir Umansky, from Prof. Hyblum's research group at the Weizmann Institute, was able to create in the laboratory the purest semiconductor material (gallium arsenic) in the world. From this material the scientists built the device in which the experiment was carried out.
These simulated particles, which have an electrical charge equal to a quarter of the charge of the electron, are created in a system where the quantum Hall effect takes place. The Hall effect takes place when electrons are placed in a two-dimensional system (surface), which is under the influence of a strong magnetic field. When electrons flow in this system, each individual electron "aspires" to continue moving straight - but the magnetic field acting on the system bends its path. Thus the magnetic field causes the accumulation of many electrons on one side of the system, perpendicular to the direction of the electric current. As the amount of electrons gathered at the edge of the surface increases, the electrons carrying a negative electric charge repel each other more strongly, and thus they resist accepting additional electrons. This creates a struggle of forces: the magnetic field pushes the electron to the edge of the system, but the many electrons that are already there repel it and influence it to return to its straight path. When these two forces reach a balance, the "new" electrons, arriving from outside the system, will indeed continue to move in a straight line, despite the attempts of the magnetic field to deflect their trajectory. Naturally, in an electronic system there is an electric field in the direction of the current flow. But in the Hall effect system - due to the influence of the magnetic field - the voltage is perpendicular to the direction of the electric current (while the voltage in the direction of the flow is zeroed). In a non-quantum system, the voltage is directly proportional to the magnetic field. On the other hand, in the quantum Hall effect operating in a two-dimensional system, and in strong magnetic fields, a surprising phenomenon occurs: the voltage remains constant even when the magnetic field is changed, and its stable value is determined by the ratio between Planck's constant and the electron charge squared, and does not depend on the properties at all The material in which the measurement is made.
In fact, there are different types of the quantum Hall effect. In one of them, known as the "non-Abelian quantum Hall effect", it is possible, under certain conditions, to build a quantum bit on which quantum computers can be based. For this, "simulated particles" with an electric charge equal to a quarter of the electron charge are needed. In addition to this, the system must have several ground states with the same energy (a ground state is a state in which the energy of the system is minimal). The third condition: the system can pass from one basic state to another, by changing the position of some of the "simulated particles". The movement of the system between the various ground states is determined according to the topology of the trajectory in which the simulated particles move, therefore a calculation method that will be based on the movement of such particles is called "topological quantum calculation". If all these conditions are met, the system becomes relatively immune to minor and uncontrollable disturbances in its environment.
Here you can ask, what will happen when they change the positions of the particles in the system. In a normal system (in which there are electrons, or simulated particles of the Leflin type), changing the positions of the particles does not change the quantum state of the system, except for the addition of an instance (phase) to the wave function of the entire system. On the other hand, when the positions of simulated particles with an electric charge equal to a quarter of the charge of the electron are exchanged, in a two-dimensional system where the non-Abelian quantum Hall effect takes place, a new phenomenon is created: the exchange of the positions of two such particles will move the entire system to a completely different quantum state (and not only for adding an instance to the wave function of the system). It is the ability to make such a fundamental difference in a system that may allow this system to function as the basis for a quantum computer. The scientists hope that a better understanding of this unique phenomenon will help progress towards the development of quantum computers.
