Author: workhouse123

Let’s try to shed some light onto the matter of quantum information by defining “information” as something that is encoded in the state of a physical system. As we have discussed, information may be encoded in the voltage on a line, a specific polarization of light, the side of a coin facing up, or vibrations…

It isn’t easy at all to understand how a bit that is both a digital one and a digital zero at the same time could be used to convey or process data. In fact, the perfectly random outcome of measuring such a bit is now used to generate random streams of numbers. The random-number function…

So far, we have explored the fundamentals of quantum physics, perhaps paying a bit too much attention to its mind-boggling philosophical implications. In the real world of academic and industrial physics however, quantum mechanics is applied very successfully to the solution of physics problems and in the development of electronic devices without the need for…

There are a number of experimental problems or “loopholes” that may affect the validity of results in Bell test experiments conducted with the type of apparatus we just described. The main challenge relates to the low detection efficiency of optical systems, and the way in which it affects the “fair sampling” of coincidences that could…

In 1982, French physicist Alain Aspect was able to run the first experimental test of Bell’s Inequality.50 Aspect used a very complex entangled source in which calcium atoms (in an atomic jet) are pumped by a two separate lasers.51 Using the CHSH form of Bell’s Inequality, Aspect was looking for the value of a certain coincidence statistical…

Our single-photon experiments (Figure 33, Figure 90, Figure 121, Figure 125, and Figure 132) have all used a highly attenuated laser beam to produce single photons. However, a precise analysis of this method shows that we could be assured that single photons fly through the apparatus only if the source photons are completely independent of each other. But photons…

Each photon in an entangled-photon pair is just a photon, and like any other photon, it can be detected using the type of methods that we used in chapter 2 (Figure 33) to detect individual photons. However, recall that the quantum efficiency of the PMT probe that we built (Figure 30) was quite low, even…

Before we go any further, we want to warn you that many of the experiments described in this chapter are out of the budget of many enthusiasts. This is because applications involving quantum entanglement are in the early stages of development, so the specialized crystals and detectors are not yet mass-produced. However, we feel that…

The debate between Einstein and Bohr continued for decades regarding what “reality” meant in the context of quantum mechanics. Einstein and his followers insisted that an objective reality exists whether it is observed or not. Their most powerful argument was explained in the EPR paper, in which Einstein and his colleagues proposed that “elements of…

The thought that an objective reality does not exist independently of an observer troubled Einstein very much. In opposition to Bohr’s group in Copenhagen, Einstein believed that the fact that quantum mechanics could only provide an answer in terms of probability meant the theory was incomplete. This was a lively discussion he maintained with Bohr…