Researchers in Canada have found a way make a key building block for quantum computing from a custom photonics chip and off-the-shelf components intended for use in telecommunications equipment.
They have built a chip that can create entangled pairs of multicolored photons. The result is that they can be manipulated as two “qudits,” quantum computing digits, that can each hold 10 possible values.
Where classical computers operate on values in sequence, quantum computers are able to express all possible values of a variable simultaneously, collapsing to the “right” answer at the end of the calculation. Not all computing problems benefit from this treatment, but it is particularly useful in the factorization of large numbers, necessary for cracking many forms of encryption.
The storage elements quantum computers are made from are inherently unstable, and must be linked in a process known as entanglement in order to work together. The more of them there are, the harder it is to keep them all entangled and functioning for long enough to perform a calculation.
The simplest quantum element is the two-dimensional qubit, a quantum bit, which can simultaneously hold two values (0 and 1). With six qubits, a quantum computer could hold any or all of 64 (2 to the power 6) possible values.
But that requires maintaining the quantum state of six elements.
In July 2016, Russian scientists suggested that, instead of building quantum computers with qubits, it would be easier to maintain a smaller number of qudits, each able to hold a greater range of values. They showed how to make a five-dimensional qudit, which would have greater computing power than a quantum computer with two qubits.
Now the Canadian researchers have demonstrated that their photonic chip can entangle two 10-dimensional qudits, storing a greater range of values than a six-qubit quantum computer, but requiring the stabilization of only two elements.
Using the same chip, they say, it should be possible to generate two entangled qudits able to hold 9,000 or more values — the equivalent of a 12-qubit computer.
By way of comparison, IBM hitched up a 16-qubit computer to its computing cloud back in May, inviting scientists to share time on it to test quantum computing algorithims.
Google, meanwhile, hopes to have an operational 49-qubit quantum computer by the end of the year.
It’s not enough merely to generate these qudits: To turn them into a quantum computer it must also be possible to manipulate them.
That can be accomplished using standard telecommunications components such as modulators and filters, according to the researchers, making the system relatively accessible.
Being able to generate multidimensional quantum computing systems in this way will open the door to faster and more robust quantum communication protocols, and more efficient and error-tolerant quantum computation, the researchers said in a paper detailing their research in the journal Nature in June.