Quantum entanglement: New research discovers potential problem with quantum computing development

Scientists say pairs of entangled photons do not actually need to originate from the same point in a crystal.

British scientists have discovered quantum mechanism that affects experiments involving quantum entanglement of light, which is essential for advanced imaging tools and quantum computers iStock

Scientists have discovered a new mechanism in quantum mechanics that challenges existing knowledge about the point at which entangled light particles originate from.

Quantum entanglement is the process where seemingly pairs or groups of counter-intuitive matter instantly affects each other, for example, the measurement of one particle on Earth instantly affecting another particle at the opposite end of the universe.

The technology is currently being researched because it potentially has a wide range of applications, including helping to develop advanced imaging tools or ultra-fast quantum computers using light particles (also known as "photons").

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Researchers from the University of East Anglia (UEA) were researching Spontaneous Parametric Down Conversion (SPDC), which is one of the main ways that pairs of entangled photons are generated, by passing a beam of photons through a crystal to create entangled photon pairs.

It has always been commonly believed that the process works by having one photon goes into the crystal, die, and then two new entangled photons are born in the same location, space and time as the one that died. However, the researchers found that the entangled pair of photons can actually originate from somewhere else in the crystal.

"The place of birth of the two new photons need not be co-located because it's possible to connect them in the vacuum field, which is a standard facet of quantum theory. Throughout our universe, there is a background of residual energy which you can't normally tap – it's an energy associated with light when there are no photons present called vacuum fluctuations," Dr David Andrews, a professor of chemistry at UEA's School of Chemistry, told IBTimes UK.

"The background is essentially borrowing the energy from the vacuum fluctuations, coupled together where the two new photons originated. It is the vacuum field that is connecting those two points."

Research could change quantum entanglement experiments

While computers today are coded using a small unit of data with a single binary value of 0 or 1, called a "bit", a quantum computer would require qubits, which are in superposition so that they can have the value of 1 or 0 at the same time.

Entangled pairs of light photons are perfect for this purpose, as each pair has properties that are linked regardless of how widely each photon is separated, and the idea is that quantum computers will be able to calculate extremely large numbers much faster than ever before.

However, if the entangled photons don't quite work the way we thought, then the vacuum field will need to be factored into any future experiments involving quantum entanglement of light. If you don't know exactly where the two photons are located, then there will be noise in the final calculation from the quantum computer or in the final image produced by an imaging tool.

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"We believe we've identified a new mechanism that hasn't been thought of before – a new aspect of quantum uncertainty that hasn't been accounted for by previous theories. There is this ultimate fuzziness in quantum mechanics. The world is more blurred than classical physics depicts, this is introducing another aspect of that uncertainty," said Andrews.

"The research invites the question of how accurate any applications that use light-based quantum entanglement."

The paper, entitled "Nonlocalized Generation of Correlated Photon Pairs in Degenerate Down-Conversion" is published in the journal Physical Review Letters.

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