A long road can be walked, or you can take a shortcut without missing the key landmarks. In quantum computing, the role of such a road is played by the evolution of a state over time: it requires ever longer chains of operations, and on a real processor it quickly drowns in noise. Physicists have found a way to compress each step of the evolution into a compact, tunable circuit while maintaining accuracy above 99%.
It was unclear whether accurate energies of quantum systems could be extracted from real dynamics on a noisy processor without resorting to deep circuits with ancillary qubits. It turns out that variational compression of each evolution step followed by Fourier analysis of the time series yields an error down to 2×10⁻³ atomic units, including nearly degenerate levels. The method can already be applied to compute electronic spectra of small molecules and models of strongly correlated materials on available quantum processors.
Compressed evolution brings us back to the idea of a shortcut: instead of charting the entire path through noisy terrain, we traverse it in segments, each time checking the map and correcting our direction.
The energy accuracy of 2×10⁻³ atomic units is equivalent to an error of about 0.05 electronvolts, comparable to the thermal energy at room temperature (about 0.025 eV).
The idea of compressing quantum evolution into a compact circuit resembles the concept of 'folded dimensions' from science fiction, where complex processes are packed into simple representations to bypass the constraints of reality.