Quantum computers promise to solve problems far beyond the reach of today’s machines, but building them is incredibly difficult.
One of the biggest challenges is simply reading the information stored in quantum bits, or qubits, without disturbing them.
Now, researchers at RIKEN in Japan have developed a new amplifier design that greatly reduces noise while boosting signals, potentially helping quantum computers scale up to hundreds of qubits.
Qubits are the heart of quantum computing. Unlike ordinary bits that store either a 0 or a 1, qubits can exist in multiple states at once.
This allows quantum computers to perform certain calculations much faster than classical computers. However, qubits are extremely fragile.
The act of measuring them can introduce noise and interference that hides or even destroys the information they contain.
To read qubits accurately, scientists use special devices that amplify the tiny microwave signals coming from them.
These amplifiers must be extremely sensitive, adding as little extra noise as possible while still producing a strong signal.
They also need to operate using very low energy, sometimes just a single microwave photon, and ideally should be able to read several qubits at the same time.
A device called a Josephson traveling-wave parametric amplifier has long been considered one of the most promising tools for this task.
It uses superconducting circuits made from arrays of Josephson junctions, components that can carry electrical current with zero resistance at very low temperatures.
These amplifiers can provide high gain and work across multiple frequencies, making them well suited for quantum computing systems.
However, one major problem remained: noise. According to the laws of quantum physics, any amplifier that preserves the phase of a signal must add a minimum amount of noise. Previous versions of these amplifiers added more noise than theoretically necessary, limiting their effectiveness. Much of this extra noise came from materials used in their construction.
The RIKEN team found a way to solve this issue by redesigning the amplifier’s structure. Instead of using materials that absorb energy and create noise, they built a spiraling, fishbone-like waveguide that guides the signal more efficiently. This new design reduced the noise level to just 0.68 quanta, very close to the theoretical minimum allowed by quantum mechanics.
Importantly, the researchers also designed the device so it can be manufactured using techniques already available in many laboratories that build superconducting qubits. This means the improvement could spread quickly across the field without requiring entirely new equipment.
By making it easier to read qubits clearly, the new amplifier could accelerate the development of larger and more reliable quantum computers.
Systems with around 100 qubits are considered a major milestone, and advances like this bring that goal closer.
As scientists continue refining these technologies, quieter and more precise measurement tools will be essential for unlocking the full potential of quantum computing.
