In a windowless basement laboratory glowing with green lasers,

physics Prof. Chris Monroe is taking the first steps toward

cracking every code that protects data on the Internet.

His research on quantum behavior of atoms may help make possible

the first quantum computer, a technology that would theoretically

be able to quickly decrypt schemes that encode information from

credit card numbers to national security matters.

Most encryption today relies on the fact that factoring a number

— or figuring out which prime numbers can be multiplied to

get that number — is extremely difficult. For instance,

although it’s easy to get the number 15 by multiplying 5 and

3, it isn’t so simple to figure out what to multiply to get

5,681.

In fact, large numbers are so difficult to factor that it took a

team of supercomputers six months to factor a 150-digit number,

Monroe said. The computers searched through millions of numbers by

trial and error before producing their result — a task

perfectly suited for a quantum computer, which stores its

information in atoms.

“Quantum computers could factor numbers fast, if we could

ever build one,” he said. “If you could factor

efficiently, you could break codes.”

In a regular computer, each input to the computer produces a

single output. To compute something with many inputs, each input

must be processed individually, Monroe explained.

But in a quantum computer, “you can store lots of numbers

in the same (atom),” he said. “You can have one atom in

lots of different states at the same time, and each state could

represent a number.”

How does this work? Instead of following the normal laws of

physics, small objects like atoms obey the laws of quantum

mechanics, which allow these objects to behave both as particles

and waves. Since a wave can occupy several positions at the same

time, a quantum object can exist in multiple states at once.

This means that each atom in a quantum computer — called a

quantum “bit,” or qubit — could represent

multiple inputs simultaneously. Unlike in a regular computer, where

each bit represents either a 0 or a 1, each qubit can denote 0, 1

or both 0 and 1 at the same time.

To understand how quantum objects like atoms behave, Monroe and

his research group study single atoms trapped in a vacuum. The

atoms must be studied in a vacuum because, through an oddity of

quantum physics, they only exhibit quantum behavior when they are

neither observed nor in contact with other matter.

“We use trapped ions — these are atoms with an

electron stripped off, so it’s a charged atom,” said

Rackham student Patty Lee, one of Monroe’s graduate students.

The charged ions can then be trapped and manipulated using an

electric field, she said.

Lasers are used to observe the atoms after manipulation, and to

change their state if necessary, Lee added.

In March, Monroe’s group made a particularly important

advance. They managed to show “entanglement” between a

photon, or a particle of light, and an atom. Entanglement means

that the atom’s state and the photon’s state are linked

— if the photon is observed in one state, the atom must also

exist in that state at the moment the photon is observed.

Monroe’s group is one of only three groups in the world

that have shown entanglement between particles, Lee said. The work

was published in the March issue of the journal Nature.

Entanglement is important for quantum computing because it

allows simultaneous control of many particles, said Rackham student

Mark Acton, another of Monroe’s students. Chains of entangled

qubits can represent many large numbers at once by denoting many

states of 0 and 1.

“If you had many ions entangled, if you do something to

one of them, it affects all the others,” Acton said.

“You don’t have to go through and (manipulate) all 100

of them. You can just do something to one of them.”

Despite such progress, Monroe remains modest about the future of

his work. “This is all really speculative stuff,” he

said. A real quantum computer may still be decades away, he added,

or eventually be proved impossible.

If theory becomes reality, though, it’s hard to

underestimate its importance.

“Quantum computing offers the opportunity of changing the

rules of the game,” Monroe said. “That has the

potential for revolutionizing computing.”