Even if experiments cannot yet tackle the measurement problem fully, they have much to contribute to a very hot field: quantum computing. A classical computer is built of transistors that switch between 0 or 1. In a quantum computer, however, the “transistors” remain in a superposition of 0 and 1 (called a quantum bit, or qubit); calculations proceed via interactions between superposed states until a measurement is performed. Then the superpositions collapse, and the machine delivers a final result. In theory, because it could process many possible answers simultaneously, a quantum computer would accomplish in seconds tasks, such as factoring large numbers to break codes, that would take years for a classical machine.
In December 1995 researchers successfully created quantum two-bit systems. Monroe and his colleagues crafted a logic element called a controlled- NOT gate out of a beryllium ion. The ion is trapped and cooled to its lowest vibrational state. This state and the first excited vibrational state constitute one bit. The second bit is the spin of one of the ion’s electrons. Laser pulses can force the bits into superpositions and flip the second bit depending on the state of the first bit. Other variations of gates couple two photons via an atom in a cavity or transmit an entangled pair of photons through a network of detectors.
Yet the creation of a useful quantum computer, relying on superpositions of thousands of ions performing billions of operations, remains dubious. The problem? Loss of superposition. The logic gates must be fast enough to work before the qubits lose coherence. Using data from the NIST gate experiment, Haroche and Raimond calculated in an August 1996 Physics Today article that given the gate speed of 0.1 millisecond, the bits would have to remain in a superposition for at least a year to complete a meaningful computation (in this case, factoring a 200-digit number).
Other physicists are less pessimistic, since error-correcting codes (which are indispensable in classical computing) might be the solution. “It gives you instructions on how to repair the damage,” says David DiVincenzo of the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y.
Moreover, DiVincenzo points out that a new method of quantum computation, making use of nuclear magnetic resonance (NMR) techniques, could raise coherence times to a second or more. Say a liquid—a cup of coffee—is placed in a magnetic field; because of thermal vibration and other forces, only one out of every million nuclei in the caffeine molecules would line up with the magnetic field. These standouts can be manipulated with radio waves to put their spins in a superposition of up and down. Maintaining coherence is easier here than in the other techniques because the nuclear spins undergoing the superpositions are well protected from the environment by the surrounding turmoil of seething molecules, the mad scramble of which averages out to zero. The calculating caffeine sits effectively in the calm eye of a hurricane. Two groups have recently demonstrated quantum computing by NMR, using a four-qubit version to sum 1 and 1. More complex systems, using perhaps 10 qubits, could be had by the end of the year.
The drawback is readout. With no way to detect individual spins, researchers must measure all the molecules’ spins— both qubit and nonqubit ones. Complex molecules capable of sustaining many spins are therefore “noisier” than simpler ones. “They’ll be able to do some nice stuff,” Monroe says, “but beyond about 10 bits, they’ll run into fundamental problems.” The output from 10 bits is only 0.001 as strong as that from a single bit; for 20, the output is down by one million. So the NMR technique may not enter a meaningful computational realm of at least 50 bits.
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Add CommentQuantum physics is so evident in our lives. Certain phenomenons aren't seen just because of the scales we use to evaluate them. It's like the earth moving with us. Do we feel it while on earth ? I would doubt. Or our milky way, moving so fast in its local group of galaxies.
Reply | Report Abuse | Link to thisInstead of introducing a mouse into the box, try a dog.
Reply | Report Abuse | Link to thisInside the box is a pregnant cat that eats mice and purrs oddly while on a rug. But if you bring the box to your quantum mechanic for repair, it never makes that odd purring sound.
Reply | Report Abuse | Link to thisI have to wonder about your use of the word "evident". Yes, quantum physics is necessary for the production of microchips that run our everyday lives, just as relativity is necessary for the operation of GPS satellites that many people rely on.
Reply | Report Abuse | Link to thisI wouldn't say, though, that either quantum physics or relativity is "evident". The reason that investigations into the quantum/classical boundary are so interesting is that the quantum mechanical laws underlying everything are /not/ obvious or intuitive.
By the way, I wish all SciAm articles were of the same quality as this long article by Haroche. Maybe it's because it was written by a Nobel Prize winner? Or maybe he's a Nobel winner precisely /because/ he can provide a clear and inspiring introduction to complicated topics.
http://www.scientificamerican.com/article.cfm?id=cavity-quantum-electrodynamics
Had we human beings or our measuring instruments been also of the size of quantum scales, will superposition still collapse since in that case boundary between quantum and classical will vanish? A question arises: what triggers the collapse of superposition -- measurement or difference in scale? Even more basic issue is why nature at small scales demonstrate quantum fuziness? Atoms and electrons may be quantum with respect our scales in which we or our instruments reside but if instruments are also of the size of atomic scale, both can be treated quantum or classical. In that case, measuring instrument should also show quantum fuziness. When measuring instruments and objects to be measured are of the comparable scales, the distinction between quantum and classical disappear.
Reply | Report Abuse | Link to thisIf measurement irrespective of scale difference collapses the superposition then this is really mysterious and difficult to explain. However, if scale difference between measuring instruments and object to be measured introduces de-coherence, it implies quantum superposition is all pervading in universe. This is even more mysterious. A cat may also be in superposition position w.r.t a measuring instrument of the size of a galaxy.
It appears true to its nature, understanding of quantum world may also remain in state of fuziness
Article does not seem to touch this issue. Any reader if he/she could address the issue.
I still have some questions of my own, but there's some good discussion in the SciAm article written by one of those recent Nobel Prize winners.
Reply | Report Abuse | Link to thisThe journal articles being described in it aren't all that new, so I was able to Google the list of authors for each study and find almost all of the texts published online. In the comments, I linked to a slide-show version of one of the papers it talks about the good agreement between theory and reality on how fast a given case of decoherence will happen.
http://www.scientificamerican.com/article.cfm?id=cavity-quantum-electrodynamics
Ref.5: Mr.Vinodkumarsehgal .the below topic will be of profound importance to your thoughts,it has been taken from a Bangladesh newspaper, -" The daily Star "
Reply | Report Abuse | Link to thisOne of the unsolved mysteries of contemporary science is how highly organized structures can emerge from the random motion of particles. This applies to many situations ranging from astrophysical objects that extend over millions of light years to the birth of life on Earth.
The surprising discovery of self-organized electromagnetic fields in counter-streaming ionized gases (also known as plasmas) will give scientists a new way to explore how order emerges from chaos in the cosmos. This breakthrough finding was published online in the journal, Nature Physics on Sept. 30.
"We've created a model for exploring how electromagnetic fields help organize ionized gas or plasma in astrophysical settings, such as in the plasma flows that emerge from young stars," said lead author Nathan Kugland, a postdoctoral researcher in the High Energy Density Science Group at Lawrence Livermore National Laboratory (LLNL). "These fields help shape the flows, and likely play a supporting role alongside gravity in the formation of solar systems, which can eventually lead to the creation of planets like the Earth."
"This observation was completely unexpected, since the plasmas move so quickly that they should freely stream past each other," explained Hye-Sook Park, team leader and staff physicist at LLNL. Park added that "laser-driven plasma experiments can study the microphysics of plasma interaction and structure formation under controlled conditions."
Studying astrophysics with laboratory experiments can help answer questions about astrophysical objects that are far beyond the reach of direct measurements. This research is being carried out as part of a large international collaboration, Astrophysical Collisionless Shock Experiments with Lasers (ACSEL), led by LLNL, Princeton University, Osaka University and Oxford University, with many other universities participating.
This work was performed at the OMEGA EP laser by the Lawrence Livermore National Laboratory.
I am explaining your missed inquiry Ref.21-Mr Vinodkumarsehgal's previous( Ultimo), Blog post, which is related to the above blog "7" Article.
Reply | Report Abuse | Link to thisAt physical level, when space expands, "what is that?" constituents of space which expands? In other words, whether fabric of space comprises of some physical building blocks or space is purely vacuum implying "nothing".
Your above para requires your careful analysis,the edict word -"Nothing ", is not applicable in Experimental Physics,mathematics and Space Time Cosmologies of Nature Bounds---as the pure vacuum of space always keeps topping up, with 1/2 SPIN PARTICLES,& as yet unknown Negative Mass Particles' that flit and fro, in the so called erroneous word, which misguides the factual entity and meaning of the word used as, "VACUUM IN PHYSICS."
KEEP IN MIND THAT LIGHT --confirms-that light speed appears "Constant in" any "Inertial Frame" ,
"TIME FREEZES IN CONICITY TRIANGULATION UNDER DYNAMIC INERTIA GRAVITY "
The metaphor of Schrodinger's cat certainly has its merits. It is rather disappointing however that it is still misused to drag consciousness into the discussion and to see quantum physics as scientific evidence in the context of dualism and the 'mind-matter' issue.
Reply | Report Abuse | Link to thisAs for the cat, lifting the lid, light reaching the eye and processing by the mind are all irrelevant considerations here but reappearing stubornly over and over again.
It has been proven experimentally for several decades that it is not 'observation' but rather 'observability' that determines whether superposition occurs or not. Superposition occurs only if no 'which-way' information remains, to be observed or not. The observer does not kill the cat.
The article correctly cites "Quantum rules forbid 'which-way' information and interference from coexisting" and "Decoherence does away with any special need for a consciousness or new physical forces". It balances these insights however with metaphysical considerations that contribute little to our understanding.
True, decoherence doesn't select a particular outcome, and many aspects of the collapse remain unexplained. I do not see any relation with consciousness however. Not in the old sense of "the observer killing the cat". Neither in more recent metaphysical considerations such as "how a conscious mind perceives an outcome" or what quantum physics has to do with "a better understanding of how brain and mind are related".
You are speaking of oft repeated Casmeir effect. Casmeir effect mentions of popping "in and out" of quantum particles from vacuum but does not describes about the stuff of space. Do you want to state that stuff of space comprises of these particles?
Reply | Report Abuse | Link to thisWhat is meant by "observability'? Does it amounts to the notion that when some quantum particle is observed, it is the limitation of observing instrument that it can not detect superposition and we interpret this as creation of decoherence but at ground level superposition still remains alive?
Reply | Report Abuse | Link to thisIn quantum mechanics, the most powerful principle is principle of superposition. Every state of everything is superposition of rest of all states. Schrodinger cat is dead and alive both at the same time before the observation. Observed cat is either dead or alive. observation collapses on state. This year, Nobel Prize is awarded to Dr. Haroche and Dr. Wineland for developing experimental technique to study individual quantum system in a particular quantum state.
Reply | Report Abuse | Link to thisS. N. Tiwary
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The problem is the theoretical and practical domain. in the recent years, many perspectives have been developed in the theoretical domain which have hypothesized many explanations for the phenomenon in the realm of physics. quantum theory is one such attempt. the coherence of the particles so to speak is beginning to border on absurdity. there are also some philosophical views that subscribe to such hypotheses. the result of the marriage between quantum physics and philosophy is the hypothesis of the existence of Multivers. It may be true that particles' coherence results in the simultaneity of presence in two spaces at once, but the important fact is also the decoherence of the event when a viewer sees it. it is no longer present in two possible spaces. As far as I know, what matters is the observer not the reality backstage since reality is what we perceive not what we think there is, detached from us. what does it mean that there is a multiverse but as soon as we perceive it, it becomes one? so it is one anyway. does it exist outside of us? it may, but what does it do when it is detached from our reality. it is also said that there is a link between the observer and observee. it means that the phenomena of observation is not detached from the phenomena of the observee. for us, reality is what effect us, what we see, what we end up with, what we have encoded in our formulas and so on and so forth. Do I care if in another world far beyond our reach, 1+1 =3 ? if this is the possibility, then let's just say that anything else even our wildest dreams and our most outrageous fictions can also be a possibility. when we can't set the boundary of what can be right and what can't be and where we have to stop getting absurd, science will turn into a joke and a circus. Then I can put some basic knowledge together and claim that I am not one. I have millions of clones like me filling every inch worth of space in an unknown galactic system, but can I ? what will be the practical aspect of such a wild
Reply | Report Abuse | Link to thisapocryphal claim?