But could one of physics’s most mind-bending states of matter become a workhorse for quantum technology? For the first time, researchers have successfully coupled a continuous time crystal-a quantum system that oscillates perpetually without energy loss-with an external mechanical device, offering a pathway toward quantum computers with far more stable memory and ultra-sensitive measurement tools.
The time crystal, first proposed by Nobel laureate Frank Wilczek in 2012, is defined by a repeating pattern in time rather than space. Whereas the atoms in ordinary crystals form a static lattice in their lowest-energy state, the constituents of a time crystal cycle through configurations endlessly while never leaving that ground state. Such motion, seemingly opposed to the second law of thermodynamics, can be possible in the quantum world because the system remains off-equilibrium, avoiding the entropy-maximising equilibrium constraining classical matter. “It’s just a setting in which the law of thermodynamics doesn’t apply… we’re talking about quantum systems that can remain out of equilibrium,” said Vedika Khemani, a Stanford physicist.
In the new paper in Nature Communications, Jere Mäkinen and colleagues at Aalto University have prepared their CTC from magnons quasiparticles representing collective spin excitations in a superfluid of helium-3 cooled to 130 microkelvin, a fraction above absolute zero. A short radio-frequency pulse pumps magnons into a magnetic trap, where they condense into a Bose–Einstein condensate. This condensate spontaneously breaks continuous time-translation symmetry and yields a coherent oscillation lasting for 108 cycles, or several minutes.
The breakthrough came when the time crystal was allowed to interact-when its oscillations were coupled with a nearby mechanical oscillator: surface gravity waves on the superfluid’s free surface. Such coupling in optomechanical physics allows the motion of one system to modulate the frequency of another-as occurs in gravitational-wave detectors. In this experiment, the surface oscillations altered the magnon condensate precession frequency, creating what the team calls “time-crystal optomechanics.” They could tune the nature of the coupling from quadratic to linear by changing parameters like the tilt of the liquid surface and the position of the crystal, a process that allowed for precise modulation of the oscillation.
Detailed measurements indicated that the amplitude of the modulation agreed with that expected from theoretical predictions for the optomechanical coupling, while the mechanical resonance was at about 12.5 Hz, consistent with geometry of the superfluid container. The strength of the coupling depended on whether the time crystal was near the surface or more deeply in the bulk: surface proximity produced direct trap-shape modulation, while bulk positioning introduced additional coupling via superfluid flow, which increased with temperature.
The implications are huge from the point of view of quantum engineering. CTCs inherently possess coherence much greater than that of the average qubit system. In quantum computing, this could mean memory elements holding onto their quantum states for orders of magnitude longer than any design does at present. CTCs are also periodic; since coherence survives, that periodicity could serve as a frequency comb-a highly precise, equidistant set of reference frequencies used in high-resolution spectroscopy and metrology-potentially allowing sensors that can detect very minute changes in magnetic or gravitational fields.
The analogy to optomechanics is not merely cosmetic: strong coupling in cavity optomechanics enables manipulation of mechanical modes down to the quantum limit, cooling their motion to the ground state or entangling them with optical fields. The team of Mäkinen now proposes replacing the optical cavity with a time crystal and taking advantage of its tunable frequency and long coherence to achieve similar feats in regimes that were previously inaccessible. Miniaturisation of the mechanical component to a nanofabricated resonator should provide a gain in mechanical frequency, a reduction of losses, and push the setup into the quantum limit, where applications in quantum information processing become feasible.
Most remarkably, the experiment demonstrates that coupling does not necessarily destroy a time crystal’s fragile order. By engineering the interaction carefully, the researchers sustained the oscillation while gaining control over its properties. The outcome is in contrast to the expectation that an isolated environment is an essential prelude to preserving time-crystalline behavior and suggests that hybrid architectures, where a time crystal interfaces with other quantum devices, are within reach.
Less than a decade after the first experimental demonstration of a time crystal, the field has evolved from a theoretical curiosity to an engineerable quantum subsystem. The current work from the Aalto team demonstrates that continuous time crystals could be harnessed as active components on optomechanical platforms, with possible far-reaching consequences for both quantum computing hardware and precision measurement science.
