Empty space in general is filled with silence. However, at the quantum level, emptiness is filled with unwanted noise.\u00a0\u00a0<\/p>\n
Now, a team of international researchers has found a way to use this noisy background to strengthen superconductivity\u2014the phenomenon in which a material carries electric current without resistance.\u00a0<\/p>\n
In their new study, they showed that carefully engineered vacuum fluctuations can raise the superconducting transition temperature of niobium diselenide (NbSe\u2082). \u201cThis represents the first experimental observation of vacuum-fluctuation-enhanced superconductivity,\u201d Guanghui Cheng, one of the study authors and a professor at the Chinese Academy of Sciences, said<\/a>.<\/p>\n The experiment, therefore, suggests that empty space itself could become a new tool for manipulating quantum matter, much like other efforts to push the limits of superconducting materials<\/a>.<\/p>\n Turning the quantum vacuum into a control knob<\/p>\n The challenge is that vacuum fluctuations are normally far too weak to noticeably influence the collective behavior of a macroscopic material.\u00a0<\/p>\n Quantum mechanics means even the lowest-energy state retains unavoidable fluctuations in its fields. Effects such as the Lamb shift and Casimir effect<\/a> have demonstrated that these fluctuations are physically real.<\/p>\n The researchers asked whether those fluctuations could instead be amplified and used to control superconductivity.<\/p>\n Their solution was a terahertz split-ring resonator, a structure that confines and reshapes electromagnetic fields. The researchers placed a six-layer NbSe\u2082 device inside this so-called dark cavity, creating a system in which the material\u2019s electronic behavior could interact with the cavity\u2019s fluctuating electromagnetic modes.<\/p>\n They then compared the superconducting behavior of NbSe\u2082 inside and outside the cavity. The difference was striking.\u00a0<\/p>\n \u201cWe observed that the critical temperature can increase by up to 5.4% in a six-layer NbSe2 device, while the critical current and critical magnetic field are significantly enhanced near the superconducting transition,\u201d Cheng said.<\/p>\n The team did not stop at observing the effect. They systematically changed the cavity\u2019s geometry and characteristic frequency, as well as the thickness of the NbSe\u2082, dielectric materials, and metallic strips.\u00a0<\/p>\n These tests helped rule out more ordinary explanations such as mechanical strain, material deterioration, uneven samples, and electromagnetic screening by the metal. Similar work on unusual superconducting materials<\/a> shows just how strongly superconductivity can respond to changes in its physical environment.<\/p>\n When the cavity starts talking to the superconductor<\/p>\n One clue proved especially important. The enhancement was not uniform across frequencies. Instead, it produced a resonant, peak-like response tied to the cavity\u2019s characteristic frequency. This suggested the cavity was not simply changing the environment around the material\u2014it was actively coupling to the superconducting state<\/a>.<\/p>\n The theoretical work further helped explain what was happening. The researchers suggested that the cavity\u2019s fluctuating electromagnetic field interacts with the superconducting state through virtual photons.\u00a0<\/p>\n In their model, this interaction can lower the energy of the superconducting state, making superconductivity more favorable. When the cavity\u2019s characteristic energy matches the energy scale of low-energy superconducting fluctuations, the effect becomes strongest, producing the resonant peak seen in the experiment<\/p>\n This builds on the team\u2019s earlier work<\/a>, in which they demonstrated direct control of vacuum fluctuations by reversibly switching the Casimir force from attraction to repulsion using a magnetic field.\u00a0<\/a><\/p>\n The new experiment takes the idea a step further. \u201cIn most practical physics, the vacuum serves merely as the passive stage on which phenomena play out. This work shows that the background itself can become an actor\u2014engineered to strengthen superconductivity and reshape the behavior of quantum matter,\u201d Frank Wilczek, one of the study authors and a theoretical physicist at MIT, said.<\/p>\n From unusual physics to quantum technology<\/p>\n The finding does not mean superconductors can now operate at everyday temperatures. The reported increase is modest, and the experiment was performed on NbSe\u2082 under carefully engineered cavity conditions.\u00a0<\/p>\n The researchers will need to determine how broadly the effect works and whether stronger enhancement can be achieved with different materials or cavity designs.<\/p>\n Still, the principle could prove valuable. Unlike conventional methods that rely on applying external electrical or magnetic drives, the cavity approach can influence the material without directly driving it.\u00a0<\/p>\n This kind of non-contact control of quantum systems<\/a> could eventually be relevant to superconducting quantum technologies, although substantial work remains before this laboratory effect can translate into practical devices.<\/p>\n