Why superconductors will be obscolete

[imported_Technomancer]

Yes, quantum mechanics has much to offer for the advancement of computing. One such potentiality is the effect of superconducting without a superconductor: moving electromagnetic energy through electron 'spin' states rather than kinetic movement/oscillations/whatever (they only move about 1 inch per hour along a wire @ ~ 120V). It is quite conceivable to develop processors using spintronic gates for effective current flow rather than what is used now... without the side-effect of encountering resistance to the current. Imagine a Prescott-type or GeForce 6800 processor implementing spintronics to operate at room temperature, no current loss to heat in the PSU...

Similarly, quantum entanglement has great potential, as ten thousand qubits can perform the computations of a processor with over 200 million transistors in the same amount of time through computing every possible solution/etc, making branch predicting/pipeline flushing a thing of the past. You can bet that manufacturers would want to cram their chips with hundreds of millions of qubits too, resulting in million-orders of magnitude improvements in computation capability. Entanglement would be the ultimate in direct-connect IO capability; does the CPU need some new cache? Just entangle the cache to a different position in RAM memory, and accesses to L2 and RAM can be reduced to single-digit clock cycles (as long as we're in the single-digit Ghz range). Or, we could do away with on-die cache and entangle directly to our RAM, or QRAM. A solid-state storage device would still be needed, but hopefully a new type of solid-state storage could be built through the workings of quantum mechanics. Access to main storage measured in tens, instead of millions of clock cycles, with I/O rates to keep the system humming along nicely, booting your Windows or Linux instantly, loading Half-Life 2 instantly, instant responsiveness in video-editing while multi-tasking thousands of programs (if you want). A multi-processing multi-processor that puts SONY's Cell to shame.

The primary problems are that we still don't know enough about quantum mechanics to make it all feaseable. I know that researchers in many places, including UC Berkely (ugh) have developed qubits. Problem is, they can't maintain the quantum entanglement states for long and destabilize after a time. They also don't know how to mass-produce them either. However, simple quantum computations have successfully been made with small groups of qubits (four to eight qubits) demonstrating their computational capabilities. All this in the last three years. So we're stuck with the classical physics model of hardware development for a while... but not forever, and certainly by the time I'm old people will laugh at us because our PDA/IPod/kitchen sink couldn't perform computations at 100 uta-flops.

Most place the dateline of quantum computing at 2030, I hope reality keeps to that date.

 

[DrPizza]

now, explain why superconductors will be obsolete again?
Sorry, but it sounds like you're summarizing an article you just read and are oblivious to other applications for superconductors.

 

[f95toli]

WHere did you find that information? It is basically all wrong.

1)Spintronics is a promising field, but so far it is mostly talk. Spin-based systems are dissipative, so where did you get the "no heat loss" idea from?

2) All solid-state qubits are made from superconductors, attempts have been made to use other systems but so far no one has succeded, you need the energy-gap to prevent decoherence. There are other types of qubits (NMR, ion-traps etc) but there is no way to scale them up to practical computers, for that you need solid-state devices.

3) The reason why we can not make larger quantum computers has little to do with our knowledge of QM, itis a basically an engineering challenge; most of the success over the past few years has been due to good fabrication technology and improved measurment electronics.

4) Quantum computers are not general purpose computers, they are fast only at a very limited number of tasks such as sorting and factorization; hence a QC is much slower than an ordinary computer in most cases.

5) You can not use entanglement to transfer information FTL, so I really don't see any point in trying to use it in a computer the way you describe. Besides, I seriusly doubt anything like that could ever be built and in any case you would need to cool it below 100 mK in order to prevent decoherence due to thermal flucutations.

 

[imported_Technomancer]

Originally posted by: f95toli
WHere did you find that information? It is basically all wrong.

1)Spintronics is a promising field, but so far it is mostly talk. Spin-based systems are dissipative, so where did you get the "no heat loss" idea from?

2) All solid-state qubits are made from superconductors, attempts have been made to use other systems but so far no one has succeded, you need the energy-gap to prevent decoherence. There are other types of qubits (NMR, ion-traps etc) but there is no way to scale them up to practical computers, for that you need solid-state devices.

3) The reason why we can not make larger quantum computers has little to do with our knowledge of QM, itis a basically an engineering challenge; most of the success over the past few years has been due to good fabrication technology and improved measurment electronics.

4) Quantum computers are not general purpose computers, they are fast only at a very limited number of tasks such as sorting and factorization; hence a QC is much slower than an ordinary computer in most cases.

5) You can not use entanglement to transfer information FTL, so I really don't see any point in trying to use it in a computer the way you describe. Besides, I seriusly doubt anything like that could ever be built and in any case you would need to cool it below 100 mK in order to prevent decoherence due to thermal flucutations.

Oh great, quote-war.

1: All I can say is that spacewar.com has a lot of explaining to do if it turns out that their information was a bunch of hype, however I tried looking for the sister-site that had the articles but they seem to have disappeared. Their names were something like energytech or nanotech or something.

2: Nobody's ever mentioned this before, everything I had seen before claimed that there are no stable qubits, period.

3: Maybe so, but it's still not there yet. I don't care about this one as it's just semantics.

4: I haven't seen anything to indicate this.

5: I never claimed or mentioned FTL transmission, only that entanglement would provide superior information transmission capability for increased bandwidth and reducing the latencies to our QRAM to the point that the processor wouldn't have to wait while the information is being fetched to execute more instructions.

Since you claim to have a superior understanding of quantum computing research, I'd like to know what your sources are since I can't seem to find them. Google is good for finding noise, but not what I need.

 

[soccerballtux]

blah blah blah

Its a ways off, it'll be faster than what we have now, and no, companies won't scale up immediately. They'll give us something like 20 Ghz so that everyone upgrades then the next year htey'll give us 30, then 40, then 50, then 70, and so on so they can milk us for all we're worth.

There.

 

[f95toli]

First a couple of comments

2. Qubits are never really stable, there are always sources of dissipation leading to decoherence after some time. In order to build a working QC we need that time (or times, the figures of merit are T1 and T2; look them up if you want the definition because it is a bit hard to explain what they mean) to be long enough for us to perform a certain number of operations (at least a few hundred) because then we can use error correction-techniques to occasionally "reset" the qubit without loosing the information.

3. No it is not sematics. Most of the experimental techniques and the phenomena we study in order to charachterize quantum circuitry (Rabi oscillations, Ramsey-fringes, spin-echo) have been borrowed from atomic physics; methods for manipulating the state of a quantum system using microwave pulses have been around for decades (mainly deveöloped for NMR).
Most of the theory for how to handle dissipative quantum systems was developed more than 20 years ago (Caldera-Legget formalim etc).

What Nakamura&co (the first observation of Rabi-oscillations in a solid-state qubit, 1999) did was to install a lot of filters in their cryostat and they used very good measurement techniques.

My main source of information is myself, I study solid-state qubits for a living (I am physicist) so I know a thing or two about the field.
If you want I can probably find some references but the problem is that most of it might be to complicated.

(Nielsen-Chuangis a good source of information on general properties of QC the first chapters are relatively easy to understand, we use it in a undergraduate course in quantum informatics. There are some examples of real systems but hardly anything on solid-state devices.

My advice is not to trust web-sites (or even most popular science journals) when it comes to information on QC, most writers simply do not understand the field and have a tendency to make wild claims about what can be done using a QC. There have been a few good articles in Scientific American so that might be worth looking up.