Using ‘Spooky Action at a Distance’ to Link Atomic Clocks

Syllabus: General Studies Paper 3

An experiment carried out by the University of Oxford researchers combines two unique and one can say even mind-boggling discoveries, namely, high-precision atomic clocks and quantum entanglement, to achieve two atomic clocks that are “entangled.” This means the inherent uncertainty in measuring their frequencies simultaneously is highly reduced.

What is Quantum Entanglement?

• Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance.
• In quantum physics, entanglement is a weird phenomenon described as a “spooky action at a distance” by Albert Einstein.
• It is a way of saying that the physical attributes of two independent systems, say spin or frequency, vary in tandem.

Atomic Clock

• An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. 
• This phenomenon serves as the basis for the International System of Units’ (SI) definition of a second – time taken by 9,19,26,31,770 oscillations of a caesium atom with accuracy of gaining or losing a second only once in about 20 million years.
• At the start of the 21st century, the cesium clocks that were available were so accurate that they would gain or lose a second only once in about 20 million years. 
• At present, even this record has been broken and there are “optical lattice clocks” that are so precise that they lose a second only once in 15 billion years. 
• To give some perspective, that is more than the age of the universe, which is 13.8 billion years.

Proof of Concept

• Quantum networks of this kind have been demonstrated earlier, but this is the first demonstration of quantum entanglement of optical atomic clocks.
• The key development here is that we could improve the fidelity and the rate of this remote entanglement to the point where it’s actually useful for other applications, like in this clock experiment.
• For their demonstration, the researchers used strontium atoms for the ease in generating remote entanglement. They plan to try this with better clocks such as those that use calcium.
• We can now generate remote entanglement in a practical way. At some point, it might be useful for state-of-the art systems.

Applications

• Studying the space-time variation of the fundamental constants, probing dark matter, precision geodesy, accurate time keeping in GPS, or monitoring stuff remotely on Mars etc.