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Saturday, April 16, 2016

What is quantum weirdness?



Physicists reveal a new explanation that could help build superfast advanced computers
From particles that only exist as probabilities to cats that are both alive and dead until you open a box, the strange features of quantum physics have been studied for the last hundred years.
But now two papers have been published that put these 'weird' features of the quantum world to good use.

Researchers have developed a method to quantify how useful different quantum systems might be for practical applications - and which will help us build efficient, small quantum computers.
Einstein described classical and quantum mechanics as 'two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.'
Things observed in quantum mechanics do not fit into our understanding of reality, because we observe only classical physics in our day to day lives.

One example of the strange features of quantum physics, or the rules that govern the smallest particles, is quantum superposition.
This is the property that allows an object to be in two states at the same time, which can be described by the famous Schrodinger's cat.
Quantum superposition, also known as quantum coherence, means particles can be in two states at once until a measurement takes place.
We know superposition actually occurs at the subatomic level because there are observable effects of interference, in which a single particle is demonstrated to be in multiple locations simultaneously.
For example, interference of particles in the double slit experiment.
But researchers from Nottingham and Strathclyde Universities are trying to put a measurement to these strange features.


Now, in two new papers, a team of physicists (Carmine Napoli, et al., and Marco Piani, et al.) has introduced a way to quantify the usefulness of quantum coherence by looking at this property from a different perspective.
The team has developed a new measurement method, which can be applied to different quantum systems and work out how useful it might be.
The new measurement method can answer questions like how useful a system's quantum superposition will be for a task like encoding and decoding secret messages.
In other words, the new method quantifies the advantage of using quantum mechanics.
'We introduce a new way to quantify quantum coherence, the quintessential signature of quantum mechanics, capturing the extent to which a system can live in a superposition of distinct states (like a coin being simultaneously heads and tails, or a famous cat dead and alive),' the researchers said.
The usefulness of quantum coherence can be described by a measure they introduce as the 'robustness of quantum coherence.'
Basically, this measures how easy it is to destroy a state's quantum coherence.
The concept is a specific version of a more general measure the scientists introduce called the 'robustness of asymmetry.'
When a quantum system is asymmetrical, it is possible to distinguish between different 'rotations' of the system.
Physicists can then use the system as a physical reference frame, which could be used to make extremely precise measurements that would not be possible without asymmetry.
Overall, the physicists see the results as a step forward in the quest to turn the strange features of quantum mechanics into something useful.
On top of benefiting physics applications such as quantum measurements and secure communication, the new measure could also be used to quantify quantum coherence in biological systems, like photosynthesis and bird navigation, the researchers say.
'The realisation that quantum properties can be harnessed for practical applications is presently fuelling a heated international race to develop and deploy quantum technologies,' the physicists wrote.
'This is no coincidence: the improved study and test of fundamental quantum properties and our increased ability to exploit them go hand in hand.'
http://journals.aps.org/…/ab…/10.1103/PhysRevLett.116.150502
http://arxiv.org/abs/1601.03782
http://journals.aps.org/…/abstra…/10.1103/PhysRevA.93.042107
http://arxiv.org/abs/1601.03781
http://phys.org/…/2016-04-physicists-quantify-quantum-weird…
https://pure.strath.ac.uk/…/robustness-of-asymm…/export.html