Part 3 (1/2)

In 1905 Einstein had shown that waves of light can have particle-like properties; that is, they can be described as packets of energy called photons But by the 1920s it was becoer that the opposite was also true: that particles like electrons could exhibit wavelike behavior This idea was first pointed out by French physicist Louis de Broglie, on the nobel Prize for this conjecture (We deraduate students at our university We fire electrons inside a cathode ray tube, like those coh a tiny hole, so normally you would expect to see a tiny dot where the electrons hit the TV screen Instead you find concentric, wavelike rings, which you would expect if a wave had passed through the hole, not a point particle) One day Schrodinger gave a lecture on this curious phenoed by a fellow physicist, Peter Debye, who asked him: If electrons are described by waves, then what is their wave equation?

Ever since Newton created the calculus, physicists had been able to describe waves in terer took Debye's question as a challenge to write down the differential equation for electron waves That er went on vacation, and when he came back he had that equation So in the same way that Maxwell before him had taken the force fields of Faraday and extracted Maxwell's equations for light, Schrodinger took the er's equations for electrons

(Historians of science have spent soer was doing when he discovered his celebrated equation that forever changed the landscape of er was a believer in free love and would often be accompanied on vacation by his mistresses and his wife He even kept a detailed diary account of all his nu each encounter Historians now believe that he was in the Villa Herwig in the Alps with one of his girlfriends the weekend that he discovered his equation) When Schrodinger began to solve his equation for the hydrogen atoy levels of hydrogen that had been carefully catalogued by previous physicists He then realized that the old picture of the ato around the nucleus (which is used even today in books and advertise to sy These orbits would have to be replaced by waves surrounding the nucleus

Schrodinger's work sent shock waves, as well, through the physics community Suddenly physicists were able to peer inside the atom itself, to examine in detail the waves that made up its electron shells, and to extract precise predictions for these energy levels that fit the data perfectly

But there was still a nagging question that haunts physics even today If the electron is described by a wave, then what is waving? This has been answered by physicist Max Born, who said that these waves are actually waves of probability These waves tell you only the chance of finding a particular electron at any place and any time In other words, the electron is a particle, but the probability of finding that particle is given by Schrodinger's wave The larger the wave, the greater the chance of finding the particle at that point

With these develop introduced right into the heart of physics, which previously had given us precise predictions and detailed trajectories of particles, from planets to comets to cannon balls

This uncertainty was finally codified by Heisenberg when he proposed the uncertainty principle, that is, the concept that you cannot know both the exact velocity and the position of an electron at the saiven amount of time At the quantum level all the basic laws of common sense are violated: electrons can disappear and reappear elsewhere, and electrons can be many places at the same time

(Ironically, Einstein, the Godfather of the quantum theory who helped to start the revolution in 1905, and Schrodinger, who gave us the wave equation, were horrified by the introduction of chance into fundamental physics Einstein wrote, ”Quantureat deal of respect But some inner voice tells me that this is not the true Jacob The theory offers a lot, but it hardly brings us any closer to the Old Man's secret For my part, at least, I a's theory was revolutionary and controversial-but it worked In one sweep, physicists could explain a vast nu the laws of chemistry To impress my PhD students with just how bizarre the quantum theory is, I sometimes ask them to calculate the probability that their atoms will suddenly dissolve and reappear on the other side of a brick wall Such a teleportation event is impossible under Newtonian physics but is actually allowed under quantum mechanics The answer, however, is that one would have to wait longer than the lifetime of the universe for this to occur (If you used a coer wave of your own body, you would find that it very much reseraph would be a bit fuzzy, with so out in all directions Some of your waves would extend even as far as the distant stars So there is a very tiny probability that one day you ht wake up on a distant planet) The fact that electrons can seely be many places at the same time forms the very basis of chemistry We know that electrons circle around the nucleus of an atom, like a miniature solar system But atoms and solar systems are quite different; if two solar systems collide in outer space, the solar syste into deep space Yet when atoms collide they often for electrons between theh school chemistry class the teacher often represents this with a ”s the two atoether

But what chemistry teachers rarely tell their students is that the electron is not ”smeared” between two atoms at all This ”football” actually represents the probability that the electron is in many places at the same time within the football In other words, all of chemistry, which explains the molecules inside our bodies, is based on the idea that electrons can beof electrons between two atoether Without the quantum theory, our molecules and atoms would dissolve instantly

This peculiar but profound property of the quantum theory (that there is a finite probability that even the las Adams in his hilarious novel The Hitchhiker's Guide to the Galaxy He needed a convenient way to whiz through the galaxy, so he invented the Infinite I vast interstellar distances in aaround in hyperspace” His e the odds of any quantuhly improbable events become commonplace So if you want to jet off to the nearest star systee the probability that you will rematerialize on that star, and voila! You would be instantly teleported there

In reality the quantueneralized to large objects such as people, which contain trillions upon trillions of ato in their fantastic journey around the nucleus, there are so hly speaking, why at our level substances seem solid and permanent

So while teleportation is allowed at the atoer than the lifetime of the universe to actually witness these bizarre effects on a macroscopic scale But can one use the laws of the quantu on dely, the answer is a qualified yes

THE EPR EXPERIMENT

The key to quantum teleportation lies in a celebrated 1935 paper by Albert Einstein and his colleagues Boris Podolsky and Nathan Rosen, who, ironically, proposed the EPR experiment (named for the three authors) to kill off, once and for all, the introduction of probability into physics (Be the undeniable experimental successes of the quantum theory, Einstein wrote, ”the more success the quantum theory has, the sillier it looks”) If two electrons are initially vibrating in unison (a state called coherence) they can remain in wavelike synchronization even if they are separated by a large distance Although the two electrons ht-years, there is still an invisible Schrodinger wave connecting both of the happens to one electron, then some of that information is immediately transle in coherence have soether

Let's start with two coherent electrons oscillating in unison Next, let the out in opposite directions Each electron is like a spinning top The spins of each electron can be pointed up or down Let's say that the total spin of the system is zero, so that if the spin of one electron is up, then you know automatically that the spin of the other electron is down According to the quantum theory, before youneither up nor down but exists in a nether state where it is spinning both up and down simultaneously (Once youa particle in a definite state) Next,up Then you know instantly that the spin of the other electron is down Even if the electrons are separated by ht-years, you instantly know the spin of the second electron as soon as you measure the spin of the first electron In fact, you know this faster than the speed of light! Because these two electrons are ”entangled,” that is, their wave functions beat in unison, their wave functions are connected by an invisible ”thread” or umbilical cord Whatever happens to one automatically has an effect on the other (This means, in sos instantaneously in distant corners of the universe, since our wave functions were probably entangled at the beginning of tile us) Einstein derisively called this ”spooky-action-at-distance,” and this pheno, in his ht

Originally, Einstein designed the EPR experiment to serve as the death knell of the quantuues in France performed this experi the spins of photons ereed precisely with the quantum theory Apparently God does play dice with the universe

Did infor about the speed of light being the speed limit of the universe? Not really Inforht, but the information was randoe, or Morse code, via the EPR experiht

Knowing that an electron on the other side of the universe is spinning down is useless information You cannot send today's stock quotations via this method For exareen sock, in rando has a red sock on it Then you know, faster than the speed of light, that the other sock is green Inforht, but this infor nonrandom information can be sent via this method

For years the EPR experi victory of the quantum theory over its critics, but it was a hollow victory with no practical consequences Until now

QUANTUM TELEPORTATION

Everything changed in 1993, when scientists at IBM, led by Charles Bennett, showed that it was physically possible to teleport objects, at least at the ato the EPR experiment (More precisely, they showed that you could teleport all the information contained within a particle) Since then physicists have been able to teleport photons and even entire cesium atoms Within a few decades scientists may be able to teleport the first DNA molecule and virus

Quantum teleportation exploits some of the more bizarre properties of the EPR experiment In these teleportation experiments physicists start with two atoms, A and C Let's say ish to teleport infor a third atoled with C, so B and C are coherent Now atom A comes in contact with atom B A scans B, so that the information content of atoled in the process But since B and C were originally entangled, the information within A has now been transferred to atom C In conclusion, atom A has now been teleported into atom C, that is, the information content of A is now identical to that of C

Notice that the information within atom A has been destroyed (so we don't have two copies after the teleportation) Thishypothetically teleported would die in the process But the information content of his body would appear elsewhere Notice also that atom A did not move to the position of ato, its spin and polarization) that has been transferred to C (This does not mean that atom A was dissolved and then zapped to another location It means that the information content of atoinal announceress has been fiercely coroups have attempted to outrace each other The first historic demonstration of quantuht were teleported occurred in 1997 at the University of Innsbruck This was followed the next year by experimenters at Cal Tech who did an evenphotons

In 2004 physicists at the University of Vienna were able to teleport particles of light over a distance of 600a fiber-optic cable, setting a new record (The cable itself was 800underneath the public sewer system beneath the River Danube The sender stood on one side of the river, and the receiver was on the other) One criticism of these experiht This is hardly the stuff of science fiction It was significant, therefore, in 2004, when quantuht, but with actual ato us a step closer to a more realistic teleportation device The physicists at the National Institute of Standards and Technology in Washi+ngton, DC, successfully entangled three beryllium atoms and transferred the properties of one atonificant that it roup was able to teleport calcium atoms as well

In 2006 yet another spectacular advance wasa macroscopic object Physicists at the Niels Bohr Institute in Copenhagen and the Max Planck Institute in Geras of cesiu trillions upon trillions of atoms Then they encoded information contained inside laser pulses and were able to teleport this information to the cesium atoms over a distance of about half a yard ”For the first tiene Polzik, one of the researchers, quantuht-the carrier of information-and atoress in teleportation is rapidly accelerating In 2007 yet another breakthrough was made Physicists proposed a teleportation lelethis problem could open up new vistas in teleportation

”We're talking about a bea fro somewhere else,” says physicist Aston Bradley of the Australian Research Council Centre of Excellence for Quantum Atom Optics in Brisbane, Australia, who helped pioneer a new method of teleportation

”We feel that our scheinal fictional concept,” he claiues take a beam of rubidiuht, send this beaht across a fiber-optic cable, and then reconstruct the original beam of atoms in a distant location If his claim holds up, thisblock to teleportation and open up entirely neays to teleport increasingly large objects

In order to distinguish this new method from quantum teleportation, Dr Bradley has called his , since his method also depends heavily on the quantulement) The key to this novel type of teleportation is a new state of matter called a ”Bose Einstein condensate,” or BEC, which is one of the coldest substances in the entire universe In nature the coldest temperature is found in outer space; it is 3 K above absolute zero (This is due to residual heat left over fro, which still fills up the universe) But a BEC is a ree above absolute zero, a temperature that can be found only in the laboratory

When certain forms of matter are cooled down to near absolute zero, their atoy state, so that all their ato coherent The wave functions of all the atoantic ”super ato in unison This bizarre state of matter was predicted by Einstein and Satyendranath Bose in 1925, but it would be another seventy years, not until 1995, before a BEC was finally created in the lab at MIT and the University of Colorado

Here's how Bradley and company's teleportation device works First they start with a collection of supercold rubidium atoms in a BEC state They then apply a beam of matter to the BEC (also made of rubidium atoms) These atoy state, so they shed their excess energy in the forht beaht beam contains all the quantuinal , the location and velocity of all its atoht beaht beainal matter beam

This new teleportation method has trelement of atoms But this method also has its problems It depends crucially on the properties of BECs, which are difficult to create in the laboratory Furthermore, the properties of BECs are quite peculiar, because they behave as if they were one gigantic atom In principle, bizarre quantum effects that we see only at the atomic level can be seen with the naked eye with a BEC This was once thought to be impossible

The immediate practical application of BECs is to create ”atomic lasers” Lasers, of course, are based on coherent bea in unison But a BEC is a collection of ato in unison, so it's possible to create beams of BEC atoms that are all coherent In other words, a BEC can create the counterpart of the laser, the atomic laser or matter laser, which is made of BEC atoms The commercial applications of lasers are enormous, and the commercial applications of atomic lasers could also be just as profound But because BECs exist only at teress in this field will be slow, albeit steady

Given the progress we have ht we be able to teleport ourselves? Physicists hope to teleport co years After that perhaps a DNA molecule or even a virusin principle to prevent teleporting an actual person, just as in the science fictionsuch a feat are truly staggering It takes some of the finest physics laboratories in the world just to create coherence between tiny photons of light and individual ato truly macroscopic objects, such as a person, is out of the question for a long time to coer, before everyday objects could be teleported-if it's possible at all

QUANTUM COMPUTERS

Ultimately, the fate of quantum teleportation is intimately linked to the fate of the development of quantum computers Both use the say, so there is intense cross-fertilization between these two fields Quantuital co on our desks In fact, the future of the world's economy may one day depend on such computers, so there is enories One day Silicon Valley could beco fro

Ordinary computers compute on a binary system of 0s and 1s, called bits But quantum computers are far more powerful They can compute on qubits, which can take values between 0 and 1 Think of an ato like a top, so its spin axis can point either up or down Common sense tells us that the spin of the atom can be either up or down but not both at the sae world of the quantum, the atom is described as the su up and an ato down In the netherworld of the quantum, every object is described by the sue objects, like cats, are described in this quantum fashi+on, it means that you have to add the wave function of a live cat to that of a dead cat, so the cat is neither dead nor alive, as I will discuss in greater detail in Chapter 13) Now inetic field, with the spin aligned in one fashi+on If a laser bea of atoms the laser bea the spin axis of so the difference between the inco laser beam, we have acco the flipping of many spins

Quantum computers are still in their infancy The world's record for a quantum computation is 3 5 = 15, hardly a calculation that will supplant today's supercomputers Quantum teleportation and quantu coherence for large collections of atoms If this probleh in both fields

The CIA and other secret organizations are intensely interested in quantum computers Many of the world's secret codes depend on a ”key,” which is a very large integer, and one's ability to factor it into prime numbers If the key is the product of two nuital computer more than a hundred years to find these two factors from scratch Such a code is essentially unbreakable today

But in 1994 Peter Shor of Bell Labs showed that factoring large numbers could be child's play for a quantum computer This discovery ience community In principle a quantu the security of today's computer systems into total disorder The first country that is able to build such a system would be able to unlock the deepest secrets of other nations and organizations

Some scientists have speculated that in the future the world's econoital computers are expected to reach their physical limits in terms of increased computer power sometiht be necessary if technology is going to continue to advance Others are exploring the possibility of reproducing the power of the human brain via quantuh If we can solve the probleht we be able to solve the challenge of teleportation; we y of all kinds in untold ways via quantuh is so important that I will return to this discussion in later chapters

As I pointed out earlier, coherence is extraordinarily difficult to maintain in the lab The tiniest vibration could upset the coherence of two atoms and destroy the computation Today it is very difficult to maintain coherence in inally in phase begin to decohere within a matter of nanoseconds to, at best, a second Teleportation in to decohere, thus placing another restriction on quantum coes, David Deutsch of Oxford University believes that these problems can be overcome: ”With luck, and with the help of recent theoretical advances, [a quantum computer] may take a lot less than 50 years It would be an entirely neay of harnessing nature”

To build a useful quantum computer ould need to have hundreds toin unison, an achieve Captain Kirk would be astronoley and advanced computers, it is difficult to see how this could be accomplished

So teleportation exists at the atoanic molecules within a few decades But the teleportation of a macroscopic object will have to wait for several decades to centuries beyond that, or longer, if indeed it is even possible Therefore teleporting co cell, qualifies as a Class I impossibility, one that should be possible within this century But teleporting a huh it is allowed by the laws of physics,it is possible at all Hence I would qualify that kind of teleportation as a Class II impossibility