Fundamentals of superconducting Q-bits
In order too build a quantum processor we must first understand some fundamental concepts.
When electrons are ionized the outer most electrons aka valiance electrons begin to flow freely through the lattice. , When the electrons flow they come into contact with the atoms causing resistance due to the impedance of the flow of electrons as well as heat.
Superconductivity is caused when electrical resistance vanishes and all magnetic flux fields “meaning the electrons flowing through the material” move throughout the lattice without coming into contact with atoms within the lattice causing both no resistance.
Cooper pairs are when electrons bind together forming a superconductor. As the electron flows through the lattice, the positive ions move towards the electron causing a distortion in the lattice. This creates an area of temporary excess positive charge which can attract a nearby electron to the electron causing the distortion in the lattice. When the cooper pairs form, the lattice no longer has enough thermal energy to separate the electrons.
Quantum tunneling is when a particle passes through a solid object. In particle physics we can never know the exact position or momentum of a particle. We are only really finding the probability that we will find said particle in a given spot at a given moment. This is what is known as a wave probability distribution. Particles behave as waves. So within the wave distribution some areas have a high or low probability of containing the particle.
A property of waves is that they can refract and reflect at the foundry of two different mediums. The weather the wave gets refracted or reflected depends on the angle of the wave passing through the medium. When 100 percent of the wave is reflected rather than refracted it is called total internal reflection.
At the point where the wave hits the boundary of a medium,, we will find an exponential drop off of the wave function. Meaning the wave decays exponentially. This is called an evanescent wave. IF the evanescent wave dose not decay completely before hitting the new medium, then the wave can continue to reflect through that medium.
The Josephson effect is when a super conducted current binds electrons into cooper pairs, and then these cooper pairs quantum tunnel in-between two superconductors and a resistant material bound in-between.
super conducting quantum interference devices or SQUIDS are what make up the back bone of our quantum processor. It is composed of two superconducting loops with multiple Josephson junctions interrupting the loop. Creating a resistant barrier that can only be passed through quantum tunneling.
The current of the super conducting ring has two currents. Clockwise and counter clockwise giving us our super positional state. Where ever we have electricity we have magnetism, The magnetic flux that surrounds the super conducted loop is quantized meaning it exists in discreet packets of energy described as integer multiple of the flux quantum.
When we apply a magnetic field to the outside of the ring that is 1/2 the flux of the inner ring, It creates a counter clockwise state |L> which is an exited state and thus |L>-|R> can be used to represent |1> while the ground state can be represented as |L>+|R>. We have now gone ovr the fundamental concepts needed to understand superconducting qubits. In the next article we will go over quantum chips and how we can bind multiple quebits to do interesting things.