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Entanglement is a phenomenon of quantum mechanics that has fascinated scientists since its discovery. When two particles are entangled, they become linked so that their properties are correlated, regardless of the distance between them. In other words, if we measure a property of one of the entangled particles, we can predict the measurement of the other particle with absolute certainty. This idea was first introduced by Albert Einstein, Boris Podolsky, and Nathan Rosen in their 1935 paper, known as the EPR paradox. They referred to entanglement as “spooky action at a distance” since the phenomenon seemed to defy classical physics and violate the principle of locality.

Albert Einstein didn’t believe himself

Einstein’s communication at a spooky distance refers to entangled particles affecting each other instantaneously, regardless of distance. This idea is counterintuitive because it violates the speed limit, which states that only the speed of light can travel faster than the speed of light. However, entanglement is not a form of communication, as it cannot transmit information more quickly than the speed of light. Entangled particles do not carry any information themselves; instead, they are correlated in a way that is independent of any measurement.

The concept of entanglement is familiar, and its history can be traced back to the early days of quantum mechanics. In 1927, Werner Heisenberg introduced the uncertainty principle, which states that knowing a particle’s position and momentum with absolute certainty is impossible. This principle led to the development of wave-particle duality, which suggested that particles have both wave-like and particle-like properties.

In the 1930s, Erwin Schrödinger introduced the idea of wave function collapse, which occurs when a particle is observed, and its wave function collapses into a single state. This idea led to the Copenhagen interpretation of quantum mechanics, which suggests that particles do not have definite properties until observed. However, this interpretation did not explain the phenomenon of entanglement, and it was not until the EPR paradox that entanglement became a central topic in quantum mechanics.

The EPR paradox was a thought experiment that demonstrated the non-locality of entanglement. Einstein, Podolsky, and Rosen argued that if two particles were entangled, then the measurement of one particle should immediately determine the properties of the other particle, regardless of the distance between them. They concluded that this violated the principle of locality, which states that events that are separated by space-like intervals cannot influence each other.

In the 1960s, John Bell developed a theorem that showed that the predictions of quantum mechanics are incompatible with local hidden variable theories, which attempt to explain quantum mechanics in terms of classical physics. Bell’s theorem led to a series of experiments that confirmed the non-locality of entanglement, and it is now widely accepted that entanglement is a fundamental aspect of quantum mechanics.

What about cryptography?

It is important to note that particle entanglement offers some exciting possibilities for cryptography. However, it is still a nascent technology that has yet to be fully understood and tested in practical applications. The field of quantum cryptography is still in its early stages, and much research is needed to determine its practicality and security.

One of the most promising uses for entangled particles in encryption is known as quantum key distribution (QKD). In QKD, two parties use entangled particles to generate a shared encryption key that is theoretically unbreakable. Any attempt to intercept or measure the key would alter the particles’ state, alerting the parties to the interception.

While this encryption method has shown great promise, it has limitations. Entangled particles are susceptible to their environment and can easily be disrupted by external factors such as temperature, vibration, and electromagnetic radiation. In other words, QKD is currently limited to short distances and requires specialized equipment to maintain the entanglement.

Furthermore, QKD is a partial encryption solution. It only generates a shared encryption key, which must be used with a separate encryption algorithm to protect the transmitted data. Therefore, developing both QKD and the accompanying encryption algorithms in tandem is essential to provide a genuinely secure system.

In addition to their use in quantum cryptography, entangled particles could be used for various other applications. One of the most promising applications is quantum computing.

Entangled particles can be used to create quantum bits or qubits, which are the building blocks of quantum computers. Qubits can be in a superposition of states, representing multiple values simultaneously, making quantum computers much faster and more powerful than classical computers for specific calculations. Entangled particles can also be used for quantum teleportation, which allows the transfer of quantum information from one location to another without physically moving the particles.

Another potential use for entangled particles is in quantum sensing. Entangled particles can create sensitive sensors that detect changes in magnetic fields, gravitational waves, and other physical phenomena. This concept could have a wide range of applications, from detecting underground oil and gas reserves to monitoring seismic activity.

Despite the overwhelming evidence for the reality of entanglement, some still refuse to accept it. Some people believe that the phenomenon of entanglement is just a mathematical trick, while others believe it is a hoax. However, the evidence for entanglement is so strong that it is difficult to deny its existence.

Current-day physics and astronomy

Several contemporary scientists study entangled particles, given that it is a field of great interest in modern physics. One such scientist is Anton Zeilinger, an Austrian physicist conducting groundbreaking research on entanglement and quantum communication since the 1990s. Zeilinger is mainly known for his work on quantum teleportation, which utilizes entanglement to transmit quantum states over long distances.

Another notable scientist in this field is Juan Ignacio Cirac, a Spanish physicist who has significantly contributed to studying entanglement in condensed matter systems. Cirac’s research has focused on developing theoretical frameworks to understand the behavior of entangled particles in complex systems, and his work has profoundly impacted the field of quantum information theory.

Additionally, several other contemporary scientists are actively studying entangled particles, including David Wineland, Alain Aspect, and Charles Bennett, to name just a few.

Entagled summary

Entanglement is a fundamental aspect of quantum mechanics that has fascinated scientists for nearly a century. Although its history can be traced back to the early days of quantum mechanics, it was only in the EPR paradox that entanglement became a central topic in physics. Einstein’s communication at a spooky distance refers to entangled particles affecting each other instantaneously, regardless of distance.