stevegrenard
03-22-2002, 09:35 AM
A New Form of Matter
Scientists have created a new kind of matter: It comes in
waves and bridges the gap between the everyday world of
humans and the micro-domain of quantum physics.
Listen to this story via streaming audio, a downloadable file, or get help.
March 20, 2002: It's not often that you get to be
around for the birth of a new kind of matter, but when
you do, the excitement is tremendous.
"To see something which nobody else has seen before is
thrilling and deeply satisfying. Those are the moments
when you want to be a scientist," says Wolfgang
Ketterle, a physicist at MIT and one of the first
scientists to create a new kind of matter called
Bose-Einstein condensates.
Right: Nobel prizing-winning scientists used lasers and
magnetic fields to create a new form of matter. [learn more] Image © 2002 The Nobel Foundation.
Bose-Einstein condensates ("BECs" for short) aren't like the solids, liquids and gases that we
learned about in school. They are not vaporous, not hard, not fluid. Indeed, there are no ordinary
words to describe them because they come from another world -- the world of quantum
mechanics.
Quantum mechanics describes the bizarre rules of light and matter on atomic
scales. In that realm, matter can be in two places at once; objects behave as
both particles and waves (a strange duality described by Schrodinger's
wave equation); and nothing is certain: the quantum world runs on
probability.
Although quantum rules are counter-intuitive, they underlie the macroscopic
reality we experience day-to-day. Bose-Einstein condensates are curious
objects that bridge the gap between those two realms. They obey the laws of the small even as
they intrude on the big.
Below: BECs form when the atoms in a gas undergo a transition from behaving like the "flying
billiard balls" of classical physics to behaving as one giant matter-wave. Image courtesy MIT.
A BEC is a group of a few million atoms that merge
to make a single matter-wave about a millimeter or so
across. In 1995, Ketterle created BECs in his lab by
cooling a gas made of sodium atoms to a few hundred
billionths of a degree above absolute zero -- more
than a million times cooler than interstellar space! At
such low temperatures the atoms became more like
waves than particles. Held together by laser beams
and magnetic traps, the atoms overlapped and formed
a single giant (by atomic standards) matter wave.
Says Ketterle: "Pictures of BECs can be regarded as
photographs of wave functions" -- that is, solutions to
Schrodinger's equation.
Working independently in 1995, Eric Cornell (National Institute of Standards & Technology) and
Carl Wieman (University of Colorado) also created BECs; theirs were made of super-cold
rubidium atoms. Cornell and Wieman shared the 2001 Nobel Prize with Ketterle "for the
achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early
fundamental studies of the properties of the condensates."
Bose-Einstein condensates were predicted by Indian physicist Satyendra Nath Bose and Albert
Einstein in the 1920's when quantum mechanics was still new. Einstein wondered if BECs were
too strange to be real even though he himself had thought of them.
Now we know Bose-Einstein condensates are real. And Einstein was right: they are strange.
For example, notes Ketterle, if you create two BECs
and put them together, they don't mix like an ordinary
gas or bounce apart like two solids might. Where the
two BECs overlap, they "interfere" like waves: thin,
parallel layers of matter are separated by thin layers of
empty space. The pattern forms because the two
waves add wherever their crests coincide and cancel
where a crest meets a trough -- so-called
"constructive" and "destructive" interference,
respectively. The effect is reminiscent of overlapping
waves from two stones thrown into a pond.
Above: A picture of overlapping Bose-Einstein condensates. These shadows reveal an "interference
pattern" -- a tell-tale sign of wave behavior. Image courtesy MIT.
"That means ... we have the remarkable effect that an atom (in one BEC) plus an atom (in another
BEC) gives no atom. It's destructive interference," says Ketterle. "Of course we didn't destroy
matter, it just appeared somewhere else in the pattern, so the total number of atoms is
conserved."
Not all atoms can form Bose-Einstein condensates -- "only those that
contain even numbers of neutrons plus protons plus electrons," says
Ketterle. Ketterle made his BECs from sodium atoms. If you add the
number of neutrons, protons and electrons in an ordinary sodium atom,
the answer is 34 -- an even number suitable for Bose-Einstein
condensation. Atoms or isotopes of atoms with odd sums can't form
BECs. Strange, but true.
Right: MIT's Wolfgang Ketterle, 2001 Nobel laureate.
One of the most extraordinary aspects of Bose-Einstein condensates is
that they are quantum creatures big enough to see. And there lies much of their promise. Many of
today's cutting-edge technologies -- smaller, faster computer chips, micro-electro-mechanical
systems (MEMS) and quantum computers -- lie in the twilight zone between the quantum world
and the macroscopic world. Scientists hope that studying BECs will advance those technologies
and create others.
Ketterle is already experimenting with one: a pulsed atom-laser.
"In an ordinary gas, atoms move around randomly, they flit around in all directions. But in a BEC,
all the atoms march lock-step," Ketterle explains. "They are just one single matter-wave
propagating in one direction."
Atom-lasers are akin to light-lasers, which are beams of photons that
likewise "march lock-step." But there are differences: For instance,
atom-laser beams have mass so they will bend downward in Earth's
gravitational field. Light-laser beams are massless; they bend, too, but the
effect is very small. Furthermore, light-lasers pass through air with ease.
Atom-laser beams will be substantially scattered by air molecules.
Left: Atom-laser pulses produced in Ketterle's lab. The curved shape of the
pulses was caused by gravity and forces between the atoms. [more]
"Atom lasers need a vacuum to retain their properties," notes Ketterle.
As a result they won't be used in the same way as light-lasers. They won't
improve CD players or supermarket scanners, for instance. But
atom-lasers will doubtless find uses of their own -- "like better atomic
clocks [which will improve spacecraft navigation -- a boon to NASA], atomic optics or very fine
lithography," says Ketterle.
Who knows where BECs will lead? After all, humans evolved on this planet with solids, liquids
and gases all around, and we're still figuring out innovative uses for them. With Bose-Einstein
condensates ... we're just getting started.
Scientists have created a new kind of matter: It comes in
waves and bridges the gap between the everyday world of
humans and the micro-domain of quantum physics.
Listen to this story via streaming audio, a downloadable file, or get help.
March 20, 2002: It's not often that you get to be
around for the birth of a new kind of matter, but when
you do, the excitement is tremendous.
"To see something which nobody else has seen before is
thrilling and deeply satisfying. Those are the moments
when you want to be a scientist," says Wolfgang
Ketterle, a physicist at MIT and one of the first
scientists to create a new kind of matter called
Bose-Einstein condensates.
Right: Nobel prizing-winning scientists used lasers and
magnetic fields to create a new form of matter. [learn more] Image © 2002 The Nobel Foundation.
Bose-Einstein condensates ("BECs" for short) aren't like the solids, liquids and gases that we
learned about in school. They are not vaporous, not hard, not fluid. Indeed, there are no ordinary
words to describe them because they come from another world -- the world of quantum
mechanics.
Quantum mechanics describes the bizarre rules of light and matter on atomic
scales. In that realm, matter can be in two places at once; objects behave as
both particles and waves (a strange duality described by Schrodinger's
wave equation); and nothing is certain: the quantum world runs on
probability.
Although quantum rules are counter-intuitive, they underlie the macroscopic
reality we experience day-to-day. Bose-Einstein condensates are curious
objects that bridge the gap between those two realms. They obey the laws of the small even as
they intrude on the big.
Below: BECs form when the atoms in a gas undergo a transition from behaving like the "flying
billiard balls" of classical physics to behaving as one giant matter-wave. Image courtesy MIT.
A BEC is a group of a few million atoms that merge
to make a single matter-wave about a millimeter or so
across. In 1995, Ketterle created BECs in his lab by
cooling a gas made of sodium atoms to a few hundred
billionths of a degree above absolute zero -- more
than a million times cooler than interstellar space! At
such low temperatures the atoms became more like
waves than particles. Held together by laser beams
and magnetic traps, the atoms overlapped and formed
a single giant (by atomic standards) matter wave.
Says Ketterle: "Pictures of BECs can be regarded as
photographs of wave functions" -- that is, solutions to
Schrodinger's equation.
Working independently in 1995, Eric Cornell (National Institute of Standards & Technology) and
Carl Wieman (University of Colorado) also created BECs; theirs were made of super-cold
rubidium atoms. Cornell and Wieman shared the 2001 Nobel Prize with Ketterle "for the
achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early
fundamental studies of the properties of the condensates."
Bose-Einstein condensates were predicted by Indian physicist Satyendra Nath Bose and Albert
Einstein in the 1920's when quantum mechanics was still new. Einstein wondered if BECs were
too strange to be real even though he himself had thought of them.
Now we know Bose-Einstein condensates are real. And Einstein was right: they are strange.
For example, notes Ketterle, if you create two BECs
and put them together, they don't mix like an ordinary
gas or bounce apart like two solids might. Where the
two BECs overlap, they "interfere" like waves: thin,
parallel layers of matter are separated by thin layers of
empty space. The pattern forms because the two
waves add wherever their crests coincide and cancel
where a crest meets a trough -- so-called
"constructive" and "destructive" interference,
respectively. The effect is reminiscent of overlapping
waves from two stones thrown into a pond.
Above: A picture of overlapping Bose-Einstein condensates. These shadows reveal an "interference
pattern" -- a tell-tale sign of wave behavior. Image courtesy MIT.
"That means ... we have the remarkable effect that an atom (in one BEC) plus an atom (in another
BEC) gives no atom. It's destructive interference," says Ketterle. "Of course we didn't destroy
matter, it just appeared somewhere else in the pattern, so the total number of atoms is
conserved."
Not all atoms can form Bose-Einstein condensates -- "only those that
contain even numbers of neutrons plus protons plus electrons," says
Ketterle. Ketterle made his BECs from sodium atoms. If you add the
number of neutrons, protons and electrons in an ordinary sodium atom,
the answer is 34 -- an even number suitable for Bose-Einstein
condensation. Atoms or isotopes of atoms with odd sums can't form
BECs. Strange, but true.
Right: MIT's Wolfgang Ketterle, 2001 Nobel laureate.
One of the most extraordinary aspects of Bose-Einstein condensates is
that they are quantum creatures big enough to see. And there lies much of their promise. Many of
today's cutting-edge technologies -- smaller, faster computer chips, micro-electro-mechanical
systems (MEMS) and quantum computers -- lie in the twilight zone between the quantum world
and the macroscopic world. Scientists hope that studying BECs will advance those technologies
and create others.
Ketterle is already experimenting with one: a pulsed atom-laser.
"In an ordinary gas, atoms move around randomly, they flit around in all directions. But in a BEC,
all the atoms march lock-step," Ketterle explains. "They are just one single matter-wave
propagating in one direction."
Atom-lasers are akin to light-lasers, which are beams of photons that
likewise "march lock-step." But there are differences: For instance,
atom-laser beams have mass so they will bend downward in Earth's
gravitational field. Light-laser beams are massless; they bend, too, but the
effect is very small. Furthermore, light-lasers pass through air with ease.
Atom-laser beams will be substantially scattered by air molecules.
Left: Atom-laser pulses produced in Ketterle's lab. The curved shape of the
pulses was caused by gravity and forces between the atoms. [more]
"Atom lasers need a vacuum to retain their properties," notes Ketterle.
As a result they won't be used in the same way as light-lasers. They won't
improve CD players or supermarket scanners, for instance. But
atom-lasers will doubtless find uses of their own -- "like better atomic
clocks [which will improve spacecraft navigation -- a boon to NASA], atomic optics or very fine
lithography," says Ketterle.
Who knows where BECs will lead? After all, humans evolved on this planet with solids, liquids
and gases all around, and we're still figuring out innovative uses for them. With Bose-Einstein
condensates ... we're just getting started.