Quantum Noise: What a Superconducting Chip Breathes express
In the superconducting circuits that make up quantum computers, extra particles, quasiparticles, are born from time to time. They are like random passersby who barge into the processor's work and spoil the calculations. Scientists have learned to catch these events in real time on two neighboring qubits — superconducting elements sensitive to charge. Both qubits are connected to a common waveguide, like two microphones in the same room: if something happens nearby, both hear it.
In a calm mode, quasiparticles tunnel (leak through the energy barrier) only a few times per second. But about once a minute, a burst occurs: within thousandths of a second, the rate jumps by a factor of a thousand. Such bursts last about 7 milliseconds, like a short ring in silence. And most importantly: both qubits hear this ring almost simultaneously, meaning that errors from quasiparticles are correlated, that is, they arise in several places at once.
The authors also noticed rare events where a burst is accompanied by a charge shift on the qubit — about once an hour. This is as if a guest not only entered the room but also moved the furniture. Understanding such correlations will help build quantum processors that make fewer mistakes — because now we can see when and where the noise comes from.
Original abstract
as written by the authors arXiv:2602.01945
Quasiparticle tunneling events are a source of decoherence and correlated errors in superconducting circuits. Understanding and ultimately mitigating these errors calls for real-time detection of quasiparticle tunneling events on individual devices. In this work, we simultaneously detect quasiparticle tunneling events in two co-housed, charge-sensitive transmons coupled to a common waveguide. We measure background quasiparticle tunneling rates at the single-hertz level, with temporal resolution of tens of microseconds. Using time-tagged coincidence analysis, we show that individual events are uncorrelated across devices, whereas burst episodes occur about once per minute and are largely correlated. These bursts have a characteristic lifetime of 7 ms and induce a thousand-fold increase in the quasiparticle tunneling rate across both devices. In addition, we identify a rarer subset of bursts which are accompanied by a shift in the offset charge, at approximately one event per hour. Our results establish a practical and extensible method to identify quasiparticle bursts in superconducting circuits, as well as their correlations and spatial structure, advancing routes to suppress correlated errors in superconducting quantum processors.
Quasiparticles in a superconductor are not real particles but collective excitations that behave like particles but exist only inside the material.
In the series "Devs," a quantum computer suffers from mysterious glitches — similar to the real problem of quasiparticle bursts, except in the movie their source is alien.