A quantum computer is like an orchestra where each musician is an electron spin: its tiny magnetic moment. For the orchestra to play in harmony, the conductor must hear each musician individually. But in germanium, a material that promises to be the foundation of quantum chips, the musicians sound almost in unison: electron spins barely split in energy. The conductor can't pick out a single voice, and controlling a quantum bit becomes impossible.
Physicists long wondered why germanium behaves so quietly. It turns out the culprit is the strain in the crystal. In modern devices, germanium is compressed to better match neighboring layers. Compression suppresses the needed splitting: electron spins become indistinguishable, like strings that are too loosely tensioned. The authors of the study proposed the opposite — stretch the germanium. Then the splitting increases by hundreds of times, and each spin sounds distinctly.
Calculations show that in stretched germanium, quantum operations could be performed in hundreds of nanoseconds — faster than in many other materials. And the technology for growing such layers already exists, so new devices can be made with current equipment. This paves the way for quantum bits based on electron spins in germanium — reliable, fast, and compatible with conventional electronics.
Now the conductor can hear each musician: stretched germanium produces clear, distinct notes. The orchestra of quantum spins is ready to play its first symphony.
Germanium is a close relative of silicon, which is used to make almost all computer chips. But unlike silicon, electrons move faster in germanium, so it is considered for future high-speed transistors and quantum devices.
In Greg Egan's novel 'Quarantine', quantum computers based on spins are controlled via strain in the crystal lattice — exactly what the authors propose.