A joint research team of the Hong Kong University of Science and Technology (HKUST) and the Guangzhou-based South China Normal University has set a new record of photonic quantum memory efficiency, with experts claiming that their breakthrough would bring quantum computing one step closer to reality.

Quantum computing is the use of quantum-mechanical phenomena such as superposition and entanglement to perform computation.

Like memories in classical computers and other electrical devices in everyday use, quantum memories are essential components for future computers of its kind, which is a new generation of data processors that go by quantum mechanics laws to overcome the limitations of existing computers.

To be succinct, classical computers are binary systems whose bit is either a one or a zero, on or off, while quantum states allow for much more complex information to be encoded into a single bit, and the uncertainty around quantum states allows us to encode more information into a much smaller computer and quantum computers can process information in superposition, to speed up some computations.

The source of the power of quantum computing is that information including graphics, videos and texts is calculated in quantum bits, or qubits, to represent both 0 and 1 at the same time in a superposition of the 1 and 0 states.

With their sheer computational power, quantum computers have the potential to push boundaries of fundamental physics, help enhance cryptography, solve linear equations and unravel mysteries of cosmology, among others.

HKUST researchers say photonic quantum memories allow for the storage and retrieval of flying single-photon quantum states yet its production remains a challenge as it requires perfectly matched photon-matter quantum interface. Meanwhile, the energy of a single photon is too weak and can be easily lost into the noisy background of stray light. As a result, these problems suppress quantum memory efficiency to below 50%.

The cover of the academic journal Nature Photonics features the latest method being trialed by Hong Kong and mainland Chinese scientists to boost quantum memory efficiency. Photo: Handout

Now physicists and computer scientists at the two universities have found a novel method to boost the efficiency to over 85%, by trapping billions of rubidium atoms into a hair-like tiny space, where these atoms would be cooled down to nearly absolute zero (minus-273.15 degrees Celsius) using lasers and magnetic fields.

The team reported in a press release that they had managed to code a flying qubit on to the polarization of a single photon and store it into the laser-cooled atoms, and although the quantum memory demonstrated in the experiment was only for one qubit operation, it could still open the possibility for further research into emerging quantum technology as well as quantum supremacy.

Their finding has been published as a cover story of the authoritative academic journal Nature Photonics.

Besides quantum computing, such quantum memories can also be used as repeaters in a quantum network, laying the foundation for a new generation of a quantum-based Internet.

As of now neither large scalable quantum hardware has been demonstrated, nor have commercially useful algorithms been published, but there is an increasing amount of investment in quantum computing by governments, tertiary institutions, established companies and startups.

Google announced in 2017 that it expected to achieve quantum supremacy by the end of that year, though that did not happen. IBM said in 2018 that the best classical computers would be beaten by quantum computing on some practical task within about five years.