Intro
You have heard that an electron or photon can be found in more than one place at the same time. Such oddities arise from the fact that everything in the quantum world is based on waves and probabilities. We do not see such phenomena on a larger scale where the classical physics are valid. We can not see a car moving forward and backward at the same time. In the same way, we do not see a person both in our right hand and in our left hand. If we know the current coordinates and speed of a car, we can calculate precisely where it will be in 10 minutes. Quantum physics does not yield a single result. There are a lot of results, and the probability of each occurrence is calculated from these results. Due to such circumstances, which are contrary to our daily experience, Einstein, Dirac, and Schrödinger have come to doubt the quantum mechanics which they have contributed to the development. In fact, Schrödinger implied that his equation's accuracy was not very trustworthy, as he questioned the "Schrödinger's cat" paradox.
How Realistic Is Quantum Mechanics And Schrödinger's Cat?
Schrödinger's cat is in a closed box with a bottle containing poisonous liquid. The box also contains a radioactive substance, such as uranium, which is uncertain when it can decay. When the uranium nucleus emits alpha particles, the bottle breaks and the cat dies. For us outside the box, the cat is 50% likely dead, 50% likely to be alive. It is a must to open the box to make a full judgment about the fate of the cat. So the cat has the possibility to be both dead and alive. However, the realization of these possibilities becomes possible by observation. This situation has philosophical dimensions such as "nothing is real until we observe". But let us question the physical reality of the quantum laws, not the physical reality of the matter
If the quantum laws are valid everywhere, every time and every scale (which is what is expected from a universal law), not only the quantum scale cat but also a normal cat in daily life should have the ability to be both alive and dead at the same time. To understand how quantum laws cause this paradoxical situation, we must, first of all, understand that quantum physics is a theory of probabilities. Quantum physics is actually a theory of probability in which negative and complex numbers take place.
These numbers, are shown as a + ib because they have both real and imaginary parts. "a" is the real part, and "b" is the imaginary part. √-1, which is not available in our world like the imaginary part, is expressed by "i". Because such numbers are dominant in quantum equations, the quantum physics have different consequences from classical physics, where probabilities are expressed only by real numbers. In classical physics, we add up possibilities of a system. For example, when a coin is thrown, two situations can take place, either heads or tails, and each situation has a probability of ½. The sum of the probabilities is exactly ½ + ½ = 1 as desired.
In a quantum system, there are probabilities that squares have a sum of 1. Let's go back to the example of Schrödinger's cat where the two situations are likely to happen. The probability of a cat being alive is denoted by α, and the probability of being dead is denoted by β. Due to the structure of the quantum equations, this time the sum of the squares of α and β is 1 (α2 + β2 = 1), not the sum of α and β. The equal probability of being dead and alive can be realized by the fact that α is equal to β and each of them has a value of 1 / √2. The mathematical wave function of the mentioned cat is written as follows:
According to quantum mechanics, each object is accompanied by a wave. In this case, the pictorial expressions indicate that the material waves that correspond to cases where the cat is alive and dead while 1 / √2 gives the magnitude of these waves. The square of these sizes is defined as the probability.
The above statement is a statement that a quantum system may exist at the same time in all situations that the system may take. According to this, we can say that Schrödinger's cat is in a state where the living and dead states overlap when the box is closed. Schrodinger's cat is an example of a two-state quantum system called quantum bit: the superposition of quantum States (overlapping) applies not only to qubits but also to all quantum systems. In addition, the complex number α and β can also be negative, depending on the position of the waves relative to each other (phase).
Quantum mechanics differs from Newton mechanics and relativity laws in this respect. How can a system of such equations of imaginary and complex numbers tell us something about the matter and its correspondence t in the universe? It is surely telling!! So that quantum mechanics can explain many unprecedented phenomena such as the reactions which energize the stars, rotation of electrons around the atomic nucleus. and many more...
In quantum theory, which is a theory of probability, why do we only take the square of the quantities and add them while doing the mathematical operations on the magnitudes of the probabilities? Why don't we sum up the third or the fourth forces? The only answer to this problem is that we have to set up the equations in this way to explain the results of experiments with the matter waves such as photons or electrons. It may not be possible to say that there is no physical reality of a law that is revealed as the result of experiments, though it seems to have only mathematics at its core. Yet some scholars argue that the quantum physics should not be perceived as a physical law but as a system based on other laws. There are also analogies of quantum physics to an operating system on which various computer software can be run. Factors such as complex numbers, strange probability calculations, and superposition not being observed on a macro scale cause the quantum physics to be suspected to belong to the physical world. Believing that Quantum is indeed a phenomenon belonging to the physical world brings the expectation of superposition observation on larger scales with itself.
Observations In The Macro-Scale
Superposition can be observed first in photons and electrons, then in lasers, superconductors, nanomagnets and carbon molecules. It is not difficult to observe the quantum superposition in an electron or a photon. Because when an electron enters a magnetic field, the spin state can be in two different directions. The vibration of a light wave is limited to two different planes, perpendicular and horizontal to the direction of travel. That is, both systems are equivalent to a two-state (two degrees of freedom) quantum system. Thus, the "superposition" I mentioned above will be exhibited. This can also be shown for an atom. For example, an atom is placed in two light waves that are superposed, then one of the waves is moved to the right and the other to the left, and the atom is forced to follow both movements. In this method, the movement of the atom that is shifted left and right step by step is starting to become random after a few steps. During these steps, called quantum marching, the matter waves (the wave function that accompanies the atom) are superposed, strengthening each other at some points, and destroying each other at some points. Looking at the atom with a high-resolution microscope, it can be seen that the atom is located at two different points, one on the right and one on the left, rather than in the first place. That is, the atom is observed at two different points at the same time.
Thermal vibrations are one of the biggest obstacles to the observation of the quantum superpositions. These vibrations disturb the phase relationship between the different quantum states, preventing the superposition from being observed. Therefore, the method used to monitor the quantum effects in a system usually starts with reducing the thermal vibrations as much as possible by cooling the system.
It is desired that the system is cooled to have very little energy. By the way, according to quantum mechanics, energy is transported in packages, not continuous, and each quantum state has different energies. To switch from an energy level to a lower energy level, an energy package with the energy difference between those levels needs to be thrown out of the system. The system is cooled down to a low energy level by releasing an energy package. When it is cooled down to the lowest energy level, there is no energy other than one or two small quantum energy packs on it. As a result, the system can be made to move between the lowest energy level and the upper energy level and thus behaving like "qubit". Of course, it is difficult for researchers to obtain "qubits" from large systems while it is easy to obtain "cubits" from an atomic or molecular one. As the system grows, it becomes difficult to isolate the system from its surroundings and from the heat.
We can observe quantum discrete energy levels at the atomic scale, but not at the macroscopic scale. For example, when our bodies move, the movements do not seem discontinuous. We can not see an object only in certain specific locations, as it is in photos taken with a high-speed camera. If we write the quantum equations of a ball motion by way of the applicability of the quantum law's universality and the human scale, we can see that the distance between the different energy levels is so small that we are not able to notice it. In other words, we find that the possible energy levels are very close to each other.
Let go of a gigantic system like a ball or a human; it is a great success for scientists to be able to move the superposition beyond an atom and observe it. Simply, think of a molecule with two atoms. A molecule that is represented by a vibrating spring system that is attached to both ends of a mass and vibrates in different styles. As I mentioned above, in order to observe the superposition, it is necessary to ensure that these vibrations are at a minimum level, that is, the energy in the system should be released as much as possible. Throughout the years, many researchers have used different cooling techniques to reduce the temperature of vibrating multi-atom systems to near absolute-zero (-273 degrees Celsius).
A Novel Method
Scientists have found a wise solution to the cooling problem required to observe quantum effects in a macroscopic system. The higher the frequency of a vibrating system (the number of vibrations per second), the higher the temperature that must be chilled to descend to the lowest energy quantum level. Taking into account this relationship between frequency and temperature, the team used a diapason that vibrates 6 billion times a second. The Diapason, which has a frequency of 6 GHz (GigaHertz), consists of an aluminum nitride layer placed between two aluminum electrodes.The high thermal conductivity of aluminum nitride crystals, to be removed effectively.
However, the scientists who performed the experiment emphasize that the real secret is at high frequency. Scientists say that cooling to a very low degree cannot be done with the technologies available. However, if the diapason vibrates billions of times at very high frequency, the temperature that the vibrating object must make a transition to the base state is slightly higher than absolute zero. It is enough to cool at least a degree of 1/50 million of 1 K. Scientists have been able to do this using commercial cooling systems. The 1 micron thick and 40-micron long diapason used in the experiment consists of trillions of atoms.
As the aluminum nitride crystal is compressed and expanded under mechanical pressure, the electric field forms inside. Thus, it can generate the electric signal. The opposite is true for such materials, which are called piezoelectric. That is when they are exposed to the electric field, the material moves. As the applied voltage changes, the material contracts and expands to make some kind of vibration. This electrical feature, which Diapason has, allows it to match an electric circuit. When the diapason and the electric circuit connected to each other are cooled to 25 milliKelvin temperature and so that they both go down to the lowest quantum energy level.
But this is not the only success of this research. The real success is the ability to control the quantum states of such a system of trillions of atoms. The researchers provide this control with the qubits in the superconductor electrical circuit they connect to diapason electrodes. The innovative idea that the experiment has is reserved for this design. The electric circuit used in the experiment consists of an inductor (L), a capacitor (C) and a Josephson's joint. In an electric circuit consisting of an inductor and a capacitor, which are energy storage elements, electric energy can be circulated in certain frequencies.
LC circuits can generate a certain frequency electrical signal. The capacitor, which consists of two conducting plates separated by an insulating layer, stores the energy generated in the electric field formed in the insulating region.When the capacitor is connected to an inductor, the electric charge accumulated in the capacitor begins to flow into the inductor. The inductor, which forms the magnetic field as the changing current passing through it, begins to store the energy in the magnetic field. The events are reversed after the capacitor is discharged and all the energy is stored in the inductor. Thus, energy travels between two circuit elements.
The frequency of change can be changed by using inductor and capacitor in different characteristics. At this point, let's note that superconducting wires and materials are used in the circuit we are talking about. In the superconductor circuit, the electrons do not travel individually but in pairs (Cooper pairs), without being exposed to any resistance. One of the key elements in the circuit used is the Josephson junction. This junction consists of two superconductors with an insulating region between them. The insulated region of this junction, which houses some kind of capacitor in itself, is so narrow that the Cooper pairs can pass to the other side by quantum tunneling.
Final Words
The experimental setup in this work, which was declared as one of the most successful researches of the past years, appeared as "the quantum machine" in popular science magazines. This mechanism is called a "quantum microphone", since the energy package can be transferred from a small mechanical Diaposon to an electric circuit developed for quantum computers. We know very well that the vibration energy in the microphones is converted into electricity. The technical success of the experiment can not be denied. But the reason why experimentation is so important is that a visible system can behave like a qubit. After all, this experiment proved that the paradox of "Schrödinger's cat" was not a paradox.
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REFERENCES
- The First Quantum Machine
- Science And Technical Journal of Scientific and Technological Research Council Of Turkey
- What did Schrodinger's Cat experiment prove?
- SUPERPOSITION, INTERFERENCE AND DECOHERENCE
- Bizarre 'Schrodinger's Cat' Comes Alive in New Experiments
- First quantum effects seen in visible object
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