Development in quantum mechanics holds the promise of changing how society processes information and measurements. It is being applied to quantum computing, cryptology, and even the future “quantum internet”. In traditional computers, the data is either a 1 or 0, quantum computing works with bits called “quibits” which can also represent 1 or 0 – but simultaneously. This allows quantum computers to perform faster and calculate more advanced functions. The 2022 Nobel Prize in Physics was won by Alain Aspect, John Clauser, and Anton Zeilinger for their work in proving a longstanding quantum nature controversy. Their experiments established a quantum phenomenon known as entanglement, which is where two different particles communicate and share information instantaneously when measured – even when they are light years apart from each other. This theory had been long debated since the 1930s and its establishment will have vast changes in today’s understanding of quantum information processes.
Entanglement
Two particles are “entangled” when they form one quantum system no matter how far apart from each other they are. When a researcher is studying entanglement, they measure a property of two particles. For example, spin. Before the particles are measured they will each be in a state of superposition (state is unknown) or both be spinning “up” and “spinning down” at the same time. If the researcher then measures one particle’s spin direction, and then measures the other, they will find that the particles are correlated. If one is spinning “up”, the other is spinning “down” and vice versa. Lets take an example of two dancers – we know there are two dancers performing pirourettes and spinning but we do not know in which direction. The dancers could in reality, be spinning in both directions simultaneously – we don’t know! However, once we get to the stage we can see that the first dancer is spinning to the right and the other to the left. But if we step into the audience, the first dancer appears to be spinning to the left and the other to the right. Although the spin direction of the dancers changes depending on what we observe, the two dancers’ spins will always be correlated. The main idea and excitement of entanglement is that knowing the state of one particle tells you about the state of its pair. It is also important to note that the state of the particles can only be determined after they are measured – nothing is known before then. Although entanglement may seem strange, with Albert Einstein even calling it “spooky action at a distance”, it is a real principle.
Historical Context
Quantum mechanics arrived during the the beginning of the 20th century – sometimes called the Second Scientific Revolution. Quantum mechanics was based on Walter Heisenberg’s uncertainty principle established in 1927 – that the more accurately the position of a particle is determined, the less likely its momentum can be predicted. This means that some types of knowledge are incompatible – with preciseness of one property making the other more uncertain. Albert Einstein (although being one of the quantum theory founders) rejected the principle saying that “God did not play dice with the universe”. He tried to determine the quantum mechanics theory as incomplete by pointing out that according to the rules, measuring a particle in one place could instantaneously affect the measurements of another no matter how far they were from each other. He attributed the coordination the spins to a “hidden variable” that would align with classical physics philosophically . These two conflicting theories remained a controversial argument until now.
Prize Winning Work
In 1964, the physicist John Bell designed – but did not perform – an experiment to test whether Einstein or the quantum mechanic theory was correct. The basic idea of the experiement was to measure the spins of particles along different axes (up, down, left, right, and even randomly). If Einstein’s theory was correct and the particles already had predetermined spins, then switching the axis on the measurement would have no effect on the outcome. However if quantum mechanics was correct and entanglement was truly spooky, then switching the axis would lead to correlated spin measurements – more often than what what possible with classic theories.
In 1972, Dr. Clauser as a graduate student attempted to execute Bell’s lab in the basement at University of California Berkeley. He used two detectors to measure each particle’s polarization, with each particle having an “up” or “down” value. Each detector produced a result of a seemingly random order of ups and downs. However, when the results from both detectors were compared, they matched more than what possible with classic physics or Einstein’s laws. Despite what he and many other scientists at the time believed, the results seemed to suggest particle entanglement to be real. In 2002, Dr. Clauser himself even said “I hoped we would overthrow quantum mechanics. Everyone else thought, ‘John, youre totally nuts.”
However, Clauser’s results did have a catch, the correlations only appeared after each individual particle was measured, when the results were compared. This meant that entanglement was plausible, but could not communicate information faster than the speed of light . A theory as to why may be is that the lab equipment was leaking information to each other.
In 1982, Dr. Aspect built on Clauser’s experiments at the University of Paris by switching the direction of which the polarizations were measured every ten nanoseconds – this would make sure that the particles were in the air and moving too fast to communicate. Although Aspect was expecting Einstein to be correct, his results further established particle entanglement as true. However, a loophole in Aspect’s experiment was still possible – that the changes in direction were regular and thus predictable so theoretically sensed by the particles or detectors. Bell’s experiment would need to be further randomized to establish entanglement as true.
In 1988, Dr. Anton Zeilinger (a professor at the University of Vienna) led a team that added even more random factors to Bell’s experiment by using random number generators to change the direction of the measurements. The results again, were in alignment with the quantum mechanics theory. Critics still suggested that the experiment may have been influenced by bias or influence from underlying causes. So, in 2017 (to now) Dr. Zeilinger and his team have been performing “Cosmic Bell” experiments (named after Bell himself), where the colors of photons emitted from distant stars determine the settings of the measurements. If there was a cosmic influence, it would have had to begun years and years before the experiments and even the experimenters themselves. Thus ultimately closing all loopholes or doubt in the existence of particle entanglement.
Why Does it Matter?
The establishment of particle entanglement showed that entangled particles could be considered a single system with connected states no matter what distance apart. This supports a phenomenon known as “nonlocality” which means that a system can be affected by something infinitely faraway instantaneously. This system of nonlocality allows computer scientists to bring an entire other dimension to hyper secure code. Using a technique called independant quantum key distribution, a pair of entangled particles is distributed to two people. This creates a secure channel between the receivers with the shared properties between the particles as the code. This system would keep the code safe even from other quantum computers. Even the system of entanglement could be expanded to more than one particle, theoretically even an infinite number. In August, a research team from China led by Xuemei Gu discovered that when they placed three entangled protons around a research facility (hundreds of meters apart from each other) and simultaneously measured them, the relationship was of a three way nonlocality. This application of entanglement is just one example of how these new discoveries are paving the way for development in quantum cryptology. Entanglement can also be used for quantum teleportation – no not sci fi, but the ability for quantum computers to work and communicate simultaneously. This saves power consumption and increases the efficiency of the share of data between the computers. Entanglement even has applications in biology, leading to potential discoveries of quantum entanglements impact on the formation of protein structures within the human body. These discoveries may have potential applications in medicine and beyond. Quantum entanglement can be used for secure cryptology, efficient data transfer, and even insight to where we come from as a species. These broad applications are what make the establishment of entanglement so important.
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