What gives Quantum computers their power is the fact they use the qubit that exists in superposition which allows it to encode information in four states instead of two states as standard computers do. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today’s most powerful semiconductor driven supercomputers.
However, another property of quantum mechanics that makes them possible is known as entanglement because to make a practical quantum computer, scientists have to devise ways of making measurements indirectly to preserve the integrity of the qubit. One way of doing this is to use quantum entangled superpositioned bits resulting in each one having four values.
Entanglement is important because it allows one to remotely view the properties of the individual components of the qubit. For example, it you apply an outside force to two atoms, it can cause them to become entangled, and the second atom can take on the properties of the first atom. So, if left alone, an atom will spin in all directions. However, the instant it is disturbed it chooses one spin, or one value; and at the same time, the second entangled atom will choose an opposite spin, or value. This allows scientists to know the value of the state of an individual components of in a qubit by observing its entangled companion without actually looking at or disturbing the qubit
The fact that entanglement exists has been experimental proven beyond a shadow of a doubt. However, one must be careful not to make hasty assumptions as to why because knowing more about the physical properties of the operating environment of a device can greatly streamline the design process of everything from transistors in modern computers to the Qubit in a quantum computer.
In 1935, Einstein co-authored a paper with Podolskyâ€“Rosen which came to be called the EPR Paradox. Its intent was to show that Quantum Mechanics could not be a complete theory of nature. The first thing to notice is that Einstein was not trying to disprove Quantum Mechanics in any way. In fact, he was well aware of its power to predict the outcomes of various experiments. What he was trying to show was that there must be a "hidden variable" that would allow Quantum Mechanics to become a complete theory of nature.
The argument begins by assuming that there are two systems, A and B (which might be two free particles), whose wave functions are known. Then, if A and B interact for a short period of time, one can determine the wave function which results after this interaction via the SchrÃ¶dinger equation or some other Quantum Mechanical equation of state. Now, let us assume that A and B move far apart, so far apart that they can no longer interact in any fashion. In other words, A and B have moved outside of each other’s light cones and therefore are spacelike separated.
With this situation in mind, Einstein asked the question: what happens if one makes a measurement on system A? Say, for example, one measures the momentum value for it. Then, using the conservation of momentum and our knowledge of the system before the interaction, one can infer the momentum of system B. Thus, by making a momentum measurement of A, one can also measure the momentum of B. Recall now that A and B are spacelike separated, and thus they cannot communicate in any way. This separation means that B must have had the inferred value of momentum not only in the instant after one makes a measurement at A, but also in the few moments before the measurement was made. If, on the other hand, it were the case that the measurement at A had somehow caused B to enter into a particular momentum state, then there would need to be a way for A to signal B and tell it that a measurement took place. However, the two systems cannot communicate in any way!
If one examines the wave function at the moment just before the measurement at A is made, one finds that there is no certainty as to the momentum of B because the combined system is in a superposition of multiple momentum eigenstates of A and B. So, even though system B must be in a definite state before the measurement at A takes place, the wave function description of this system cannot tell us what that momentum is! Therefore, since system B has a definite momentum and since Quantum Mechanics cannot predict this momentum, Quantum Mechanics must be incomplete.
In response to Einstein’s argument about incompleteness of Quantum Mechanics, John Bell derived a mathematical formula that quantified what you would get if you made measurements of the superposition of the multiple momentum eigenstates of two particles. If local realism was correct, the correlation between measurements made on one of the pair and those made on its partner could not exceed a certain amount, because of each particle’s limited influence.
In other words, he showed there must exist inequities in the measurements made on pairs of particles that cannot be violated in any world that included both their physical reality and their separability because of the limited influence they can have on each other when they are "spacelike" separated.
When Bell published his theorem in1964 the technology to verify or reject it did not exist. However, in the early 1980s, Allen Aspect performed an experiment with polarized photons that showed that the inequities it contained were violated.
This meant that science has to accept that either the reality of our physical world or the concept of separability does not exist.
Many would prefer to assume the separability defined by Newtonian physics does not exist instead of the reality of our particle world because without that "reality" Einstein and many others believe science would have little meaning.
However, measurements Allen Aspect made on polarized photons that showed that Bells inequity was violated appeared to verify the concepts of quantum mechanics assumes the act of measuring the state of a pair of entangled particles instantly affects the other no matter how far they are apart. In other words, the Newtonian concept separability does not apply to quantum environment.
However, one must be careful not to extrapolate the unique properties of a photon like the fact that they are the only particle that moves at the speed of light to other particles that make up the qubit.
We believe Einstein, Podolsky, and Rosen were aware of this special property of a photon because they specified in the description of their experiment "two systems, A and B (which might be two free particles)â€ not just a photons because they knew that Special Relativity gives us a reasons why they would entangled which were different from those given by quantum mechanics.
Einstein told us that the observe distance between the measurement of end points of objects or particles in relative motion would be shorter in direct relationship to their speed from the perspective of those objects or particles.
In other words, the faster particles are moving relative to the observers the shorter the distance between the end points of those observations will be from their perspective. At the speed of light he tells us the distance between the end points of any and all measurements will be zero from the perspective of any particle moving at the speed of light.
However, he also told us that due to the relativistic properties space and time there is no special reference frame by which one can measure distance. Therefore, one would be justified in measuring the distance between the end points of the observation from the perspective of the photons as well as from the laboratory environment where they are being observed by humans.
Yet as was just mentioned he also tells us since photons are moving at the speed of light the distance between the end point of the measurements made between all human observers in the universe no matter where they are must be is zero. However, because all of the confirmation entanglement involves the properties of photons, we must look at the world from their perspective and not form those of human observers.
In other words, Einstein specified "two free particles" not just photons because he knew the reason they would be entangled is because the distance between the end points of all measurements made by humans from perspective of all photons would be zero therefore they would be entangled.
As was mentioned earlier the fact that entanglement exists has been experimental proven beyond a shadow of a doubt with respect to a photon. However, as is show above Einstein Theory of Relativity provides an alternating explanation as to why with respect to photons, which is just a valid as the one provided by quantum mechanics. Since it is one of the foundational concepts of quantum computing knowing which one of them is is responsible will give engineers a better understanding its strengths and limitations and will hopefully allow them to design systems that will take better advantage of them.
Copyright Jeffrey O’Callaghan 2019
The Road to Unifying
The Road to Unifying
The Road to Unifying