“Made in Jülich”: Quantum microscope

Scan­ning tun­nel­ing micro­scopes image mate­ri­als with atom­ic pre­ci­sion and are ver­sa­tile. Researchers have there­fore been using them for many years to explore the world of the nanocos­mos. Physi­cists at Forschungszen­trum Jülich have now opti­mized such a device for the study of quan­tum effects. Thanks to mag­net­ic cool­ing, their scan­ning tun­nel­ing micro­scope has no mov­ing parts and oper­ates at extreme­ly low tem­per­a­tures of up to 30 mil­likelvin with vir­tu­al­ly no vibra­tion. In the future, the instru­ment can help researchers unlock the unusu­al prop­er­ties of quan­tum mate­ri­als that are crit­i­cal to the devel­op­ment of quan­tum com­put­ers and sensors.

The region near absolute zero is par­tic­u­lar­ly excit­ing for physics. Ther­mal fluc­tu­a­tions are min­i­mized at the low tem­per­a­tures. The laws of quan­tum physics come into play, reveal­ing spe­cial prop­er­ties of mate­ri­als. Elec­tric cur­rent then flows loss­less­ly with­out any resis­tance. Anoth­er exam­ple is so-called super­flu­id­i­ty: Indi­vid­ual atoms fuse into a col­lec­tive state and move past each oth­er with­out friction.

Such extreme­ly low tem­per­a­tures are also the nec­es­sary pre­req­ui­site for explor­ing and har­ness­ing quan­tum effects for quan­tum com­put­ing. Researchers world­wide, includ­ing those at Forschungszen­trum Jülich, are cur­rent­ly pur­su­ing this goal at full speed. Quan­tum com­put­ers could be vast­ly supe­ri­or to con­ven­tion­al super­com­put­ers for cer­tain tasks. But devel­op­ment is still in its infan­cy. A key chal­lenge is find­ing mate­ri­als and process­es that make com­plex archi­tec­tures with sta­ble quan­tum bits possible.

“I believe a ver­sa­tile micro­scope like ours is the tool of choice for this fas­ci­nat­ing task because it allows imag­ing and manip­u­lat­ing mat­ter at the lev­el of indi­vid­ual atoms and mol­e­cules in a vari­ety of ways.”

- Rus­lan Temirov of Forschungszen­trum Jülich

Over years of work, he and his team have equipped a scan­ning tun­nel­ing micro­scope with mag­net­ic cool­ing for this pur­pose. “Our new micro­scope dif­fers from all the oth­ers in much the same way that an elec­tric car dif­fers from a com­bus­tion engine,” explains the Jülich physi­cist. Until now, peo­ple relied on a kind of liq­uid fuel, a mix­ture of two heli­um iso­topes, to bring micro­scopes to such low tem­per­a­tures. “Dur­ing oper­a­tion, this cool­ing mix­ture con­tin­u­ous­ly cir­cu­lates through thin tubes, which leads to increased back­ground noise,” Temirov says.

The Jülich micro­scope’s cool­ing device, on the oth­er hand, is based on the adi­a­bat­ic demag­ne­ti­za­tion process. The prin­ci­ple is not new. It was already used in the 1930s to real­ize tem­per­a­tures below 1 Kelvin in the lab­o­ra­to­ry for the first time. “To cool the device, we only change the strength of the elec­tric cur­rent flow­ing through an elec­tro­mag­net­ic coil. Our micro­scope there­fore has no mov­ing parts, and oper­ates vir­tu­al­ly vibra­tion-free,” reports Rus­lan Temirov.

The Jülich team is the first to design a scan­ning tun­nel­ing micro­scope using this tech­nol­o­gy. “The new cool­ing tech­nol­o­gy has sev­er­al advan­tages in prac­tice. Not only does the imag­ing qual­i­ty ben­e­fit, but the oper­a­tion of the instru­ment and the entire set­up are sim­pli­fied,” says insti­tute direc­tor Ste­fan Tautz. With its mod­u­lar design, the Jülich quan­tum micro­scope is also open to tech­ni­cal advances, he adds, because upgrades can be eas­i­ly imple­ment­ed. “Adi­a­bat­ic cool­ing is a real quan­tum leap for scan­ning tun­nel­ing microscopy. The advan­tages are so sig­nif­i­cant that we are now devel­op­ing a com­mer­cial pro­to­type as the next step,” explains Ste­fan Tautz. Quan­tum tech­nolo­gies are cur­rent­ly the focus of research. The inter­est of numer­ous research groups in such an instru­ment is there­fore like­ly to be assured.