"Long before it's in the papers"
January 28, 2015


World’s smallest storage space: an atomic nucleus

Oct. 24, 2008
Courtesy NSF
and World Science staff

Sci­en­tists say they’ve per­formed the ul­ti­mate miniatur­iz­a­tion of com­put­er mem­o­ry: stor­ing in­forma­t­ion at the nu­cle­us of an at­om. The break­through is a key step in bring­ing to life quan­tum com­put­ers, de­vices based on the strange pro­per­ties of sub­atom­ic part­i­cles, ac­cord­ing to the re­search­ers.

In order to perform their experiments, sci­en­tists loaded si­li­con, the grey half-moon ob­ject in the mid­dle of the tube, in­to a re­so­na­tor. The team created a sys­tem that used both the elec­tron and nu­cleus of a phos­pho­rous at­om em­bed­ded in a sil­i­con crys­tal. Both the elec­tron and nu­cle­us be­haved as ti­ny quan­tum mag­nets ca­pa­ble of stor­ing quan­tum in­for­ma­tion. This al­lows in­for­ma­tion to stay in­tact for over a sec­ond, an im­por­tant thresh­old in the de­vel­op­ment of quan­tum com­put­ing. (Cour­te­sy Ste­phen Ly­on, Prince­ton Uni­ver­si­ty )

In this quan­tum world, ob­jects can ex­ist sim­ul­ta­ne­ous­ly in mul­ti­ple states: that is, they could be in two places at once, or pos­sess a num­ber of oth­er seem­ingly con­tra­dic­to­ry prop­er­ties. 

These tricks lead to the pos­si­bil­ity of so-called quan­tum com­put­ing, seen as a holy grail of com­put­ing be­cause each in­di­vid­ual piece of in­forma­t­ion, or “bit,” can have more than one val­ue at once.

A bit is a fun­da­men­tal un­it of in­forma­t­ion, rep­re­sented as a 0 or 1 in a nor­mal dig­it­al com­put­er. Put­ting bits to­geth­er cre­ates a code, which gen­er­ates or pro­cesses in­forma­t­ion. How­ev­er, a quan­tum bit, or qu­bit, could be both 1 and 0 at the same time. That means a sin­gle qu­bit has twice the pow­er of a nor­mal bit, and once qu­bits start in­ter­act­ing with each oth­er, the pro­cess­ing pow­er rises ex­po­nen­tially.

How to ma­neu­ver and con­trol quan­tum bits of in­forma­t­ion has been a ma­jor fo­cus of ex­pe­ri­menta­t­ion. Re­search­ers have been test­ing ways to iso­late a quan­tum bit from a noisy en­vi­ron­ment, pro­tect­ing its del­i­cate quan­tum in­forma­t­ion, while al­low­ing it to in­ter­act with the out­side world so that it can be ma­ni­pu­lated and meas­ured.

The sci­en­tists from Prince­ton Uni­ver­s­ity, Ox­ford Uni­ver­s­ity and the De­part­ment of En­er­gy’s Law­rence Berke­ley Na­tional Lab­o­r­a­to­ry in Cal­i­for­nia re­ported a so­lu­tion in this week’s is­sue of the re­search jour­nal Na­ture.

The team de­scribed a sys­tem that used two com­po­nents of an an at­om em­bed­ded in a sil­i­con crys­tal: the elec­tron and nu­cle­us. Both parts be­haved as ti­ny quan­tum mag­nets ca­pa­ble of stor­ing quan­tum in­forma­t­ion, en­cod­ed in their spe­cif­ic state.

In­side the crys­tal, the elec­tron “cloud,” or the ar­ea gen­er­ally in­hab­it­ed by the elec­tron, was more than a mil­lion times big­ger than the at­om’s nu­cle­us, with a mag­net­ic field a thou­sand times stronger. The size of the elec­tron cloud made it well-suit­ed for ma­nipula­t­ion and meas­ure­ment, but not so good for stor­ing in­forma­t­ion be­cause of elec­tron in­sta­bil­ity. To over­come the prob­lem, re­search­ers moved the in­forma­t­ion in­to the nu­cle­us where it sur­vived much long­er. 

“No­body really knew how long a nu­cle­us might hold quan­tum in­forma­t­ion in this sys­tem,” said Steve Ly­on, lead­er of the Prince­ton team. “With crys­tals pains­tak­ingly grown by the Berke­ley team and very care­ful meas­ure­ments, we were de­light­ed to see mem­o­ry times ex­ceed­ing the thresh­old.”

The team found that in­forma­t­ion stored in the nu­cle­us sur­vives al­most two sec­onds. Be­fore the new stu­dy, the longest re­search­ers could pre­serve quan­tum in­forma­t­ion in sil­i­con was less than one-tenth of a sec­ond. Oth­er re­search­ers stu­dying quan­tum com­put­ing re­cently cal­cu­lat­ed that if a quan­tum sys­tem could store in­forma­t­ion for at least one sec­ond, other tech­niques could then pro­tect that da­ta for an in­def­i­nite time. 

“The elec­tron acts as a middle-man be­tween the nu­cle­us and the out­side world,” said John Mor­ton, a re­search fel­low at Ox­ford. “It gives us a way to have our cake and eat it—fast pro­cess­ing speeds from the elec­tron, and long mem­o­ry times from the nu­cle­us.”

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Scientists say they’ve performed the ultimate miniaturization of computer memory: storing information at the nucleus of an atom. The breakthrough is a key step in bringing to life quantum computers, devices based on the theory of quantum mechanics, researchers say. In the quantum world, the size scale of subatomic particles, objects can exist simultaneously in multiple states: that is, they could be in two places at once, or possess a number of other seemingly contradictory properties. These tricks lead to the possibility of so-called quantum computing, seen as a holy grail of computing because each individual piece of information, or “bit,” can have more than one value at once. A bit is a fundamental unit of information, represented as a 0 or 1 in a normal digital computer. Putting bits together creates a code, which generates or processes information. However, a quantum bit, or qubit, could be both 1 and 0 at the same time. That means a single qubit has twice the power of a normal bit, and once qubits start interacting with each other, the processing power rises exponentially. How to maneuver and control quantum bits of information has been a major focus of experimentation. Researchers have been testing ways to isolate a quantum bit from a noisy environment, protecting its delicate quantum information, while allowing it to interact with the outside world so that it can be manipulated and measured. The scientists from Princeton University, Oxford University and the Department of Energy’s Lawrence Berkeley National Laboratory in California reported a solution in this week’s issue of the research journal Nature. The team described a system that used two components of an an atom embedded in a silicon crystal: the electron and nucleus. Both parts behaved as tiny quantum magnets capable of storing quantum information, encoded in their specific state. Inside the crystal, the electron “cloud,” or the area generally inhabited by the electron, was more than a million times bigger than the atom’s nucleus, with a magnetic field a thousand times stronger. The size of the electron cloud made it well-suited for manipulation and measurement, but not so good for storing information because of electron instability. To overcome the problem, researchers moved the information into the nucleus where it survived much longer. “Nobody really knew how long a nucleus might hold quantum information in this system,” said Steve Lyon, leader of the Princeton team. “With crystals painstakingly grown by the Berkeley team and very careful measurements, we were delighted to see memory times exceeding the threshold.” The team found that information stored in the nucleus survives almost two seconds. Before the new study, the longest researchers could preserve quantum information in silicon was less than one-tenth of a second. Other researchers studying quantum computing recently calculated that if a quantum system could store information for at least one second, error correction techniques could then protect that data for an indefinite period of time. “The electron acts as a middle-man between the nucleus and the outside world,” said John Morton, a research fellow at Oxford’s St. John’s College. “It gives us a way to have our cake and eat it—fast processing speeds from the electron, and long memory times from the nucleus.”