Quantum computers tend to be labyrinthine machines the size of a fridge with large tangles of control and cooling systems. This complexity is a huge hurdle to scaling up processor power to tackle harder problems. But researchers have finally proved that a decades-old theory to simplify silicon quantum processors can work, potentially paving the way for vastly more powerful devices.
Most current quantum computers require a control wire for every qubit on a processor, which is used to change the qubit鈥檚 spin, or data state, with high-frequency, oscillating signals. Each of these wires is connected to its own microwave source called a cavity 鈥� and each has to reach into the supercooled interior of the computer.
But these control wires generate heat which has to be removed, increasing the physical size of each qubit.
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鈥淢icrowave cavities don鈥檛 really like the presence of the circuit and the circuit doesn鈥檛 really like the presence of the microwave cavity,鈥� says at the University of New South Wales, Australia. 鈥淵ou have these sensitive nanoelectronic circuits that are there to measure displacements of single electrons, and if you put this thing in a big microwave cavity and it鈥檚 been blasted with electric fields, then it doesn鈥檛 like that.鈥�
A long-standing idea suggests that, in theory, a single, less disruptive microwave source can control all of the qubits across the entire processor. Pla and his colleagues have now demonstrated this in practice. Instead of sending signals directly to each qubit as needed, qubits are brought into and out of resonance with this single signal. Crucially, the equipment needed to change the resonance already exists within the logical components of qubits, meaning that this approach will lead to processors that are far less complex.
Pla says that current quantum computers tend to be an 鈥渁bsolute mess of wiring and all sorts of control systems鈥�, but that this technology could simplify them massively.
Cutting edge quantum computers like Google鈥檚 Sycamore processor have just dozens of qubits. But practical, useful machines are likely to require thousands or millions of qubits.
Silicon quantum computers like the one used by Pla and his team use standard CMOS technology at their core like the silicon chips inside classical computers. Once the ancillary control systems that sit around them are refined, then they could be scaled up quickly.
