## First Quantum Computing Gate on a Chip 166 166

An anonymous reader writes

*"After recent success in using quantum computing for superconducting qubits, researchers from Delft have formed the first Controlled-NOT quantum gate. 'A team has demonstrated a key ingredient of such a computer by using one superconducting loop to control the information stored on a second. Combined with other recent advances, the result may pave the way for devices of double the size in the next year or two--closer to what other quantum computing candidates have achieved, says physicist Hans Mooij of the Delft University of Technology in the Netherlands. Unlike today's computers, which process information in the form of 0s and 1s, a quantum computer would achieve new levels of power by turning bits into fuzzy quantum things called qubits (pronounced cue-bits) that are 0 and 1 simultaneously. In theory, quantum computers would allow hackers to crack today's toughest coded messages and researchers to better simulate molecules for designing new drugs and materials.'"*
## Double the size of a single not gate? (Score:5, Funny)

computersare blatantly spewing out double negatives?We're not in for an unrough ride, gentlemen.

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## Imagine slashdot on a quantum server! (Score:4, Funny)

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Personally, I'd just enjoy seeing them post a picture of a dead cat as a story.

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Let's try it... -universe asplodes-

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## It depends... (Score:2)

## A solid milestone... (Score:5, Interesting)

For those wondering why this is important, the first true electronic gates were invented in the early 1920's. This predates point-contact transistors by about 20 years, invented in 1947. 60 years later, here we are with transistor computing in every aspect of our lives.

At the rate quantum computing is advancing, I think we can expect to see quantum transistors (in the lab, at least) by 2020. A true useful quantum computer may be available less than 50 years from now. Hopefully by then someone will pick up the slack and have the Linux kernel ported to the Q-CPU architecture!

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Come to think of it, arithmetic encoding is a bit like encryption...

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## Used for what? (Score:4, Funny)

At home you will use these for ever more sophisticated rendering of artificially intelligent virtual reality porn.

At work it will be more useful in the advanced simulation of a mechanical process for imprinting letter glyphs on sheets of wood fiber.

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The trick is going to be figuring out the right first interaction to generate the recipe you're searching for.

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IIRC, quantum computers have one killer app, which is that they can simulate other quantum systems (i.e. Stuff). If you try simulating a lump of high temperature superconductor on a classical computer you won't get very far, but on a quantum computer you just might.

#disclaimer: This is slashdot, so I reserve the right to have been talking out of my a(r?)s[se].

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Regex pedantry here, but you're being overly permissive - you allow semantically invalid words: as, ars & arss.

As a side-note, if you like hearing from your local regex pedant, please remember to donate g(ener|ratuit)ously: we survive only through your funding

...it's like I know I should be ticking 'Post Anonymously' but I just can't stop myself

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No they don't. The only matches are ass, ase, arss and arse, but your point still stands. When being a pedant, it's also polite to provide a correction. The regex they were after is: a(rse|ss).

At least tick "No Karma Bonus", please

## Really freaking fast processing by estimation (Score:3, Interesting)

## Re:A solid milestone... (Score:4, Funny)

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Come to think of it, arithmetic encoding is a bit like encryption...

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However, the only kind of problems for which we would use blind search are very hard and take a very long time already, and the square root of a very slow algorithm is usually still a very slow algorithm. While they are "interesting" problems, they are largely esoteric in nature. Any practical applications of quan

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Esoteric, maybe (it'll be a computer in a lab, not a PC), but usable nonetheless.

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Isn't that a little short-sighted of you? Who's going to have PC's in 20 years anyway? I seem to recall adverts from the 60's (from archives only I wasn't born until '80) that say something like "eventually Computers will be small enough to fit into a single room."

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Like transistors, tubes are just amplifiers. Contrary to popular belief, both are analogue components, but they have quite different responses to changes in current (the graphs are a different shape). Many people consider tube amplifiers to produce bette

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Really? I know they can get close, and it's possible to prove that power must be consumed to change state, but I'd love to see a device with no leakage. Gates such as those used in NAND flash devices (dual MOSFETs) get pretty close, but I'm pretty sure even they leak, especially on read operations.

You got me there. I'd forgotten about leakage across the insulating layer due to quantum tunneling. OTOH, a vacuum tube doesn't work well without power to the heating element. Come to think of it, though, one could still get current flow at ambient temperatures; It just wouldn't be nearly as large as when you have a hot cathode.

My point is that quantum computers are not just special transistors with slightly different properties. They really are a completely different thing. You're never going to make an amplifier out of quantum gates, and you're never going to make a quantum computer out of transistors

Point taken and noted. I'm still not very clear on how quantum computing works, but I'm looking forward to reading more discussions like this one in the future.

## Re:A solid milestone... (Score:5, Informative)

Keep in mind that this is a Controlled-NOT gate (a two-input gate) and not a simple NOT gate (a one-input gate). It has been proven that if you can implement two-qubit C-NOT and arbitrary one-qubit operations, you can implement a universal quantum computer (that is, one that can run an arbitrary "quantum program").

There is a deeper reason for quantum computers not to use AND/OR gates, which is their irresibility (AND and OR are two-input to one input gate, which makes them irreversible). Quantum Mechanics is intrinsically reversible, so a quantum computer should be reversible too and that's why it is not common to hear about Quantum AND or Quantum OR.

Pablo B.

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Is there a reason why it's called a NOT gate rather than XOR ? Is there some quantum wierdness that makes the thing asymmetric and causes A-inverts-B to mean something different to B-inverts-A ?

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I guess it's mostly historical, and that XOR is usually associated with a two-input/one-output gate. Controlled-NOT looks pretty intuitive (the target is negated only if the control is 1), but probably XOR is better because A-inverts-B is exactly the same as B-inverts-A (which seems counterintuitive when you think o

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I guess it's mostly historical, and that XOR is usually associated with a two-input/one-output gate. Controlled-NOT looks pretty intuitive (the target is negated only if the controlQuantum mechanics being unitary and thus reversible, it's important that your gates be reversible, too*. CNOT is two-input, two-output, and is reversible. XOR is two input, one output, and is clearly not reversible (given the output you can't reconstruct the inputs). This is why people use CNOT for quantum computing--XOR wouldn't

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There is a fundamental difference though. The classical 'equivalent' of a C-NOT is indeed just an XOR gate where one of the inputs is duplicated as the second output line. This follows a common tool in classical circuits, where one output line can drive a large number of different inputs. You never need a two-output gate in a classical circuit because you could always produce the same effect by having two one-output gates and copying the inputs to each gate.

But in a quantum circuit, there is a fundam

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You made that up, didn't you? Even the Wikipedia article you mention doesn't say anything about a 2-input gate called 'NOT'. I've never heard of A NOT B as shorthand for A AND (NOT B) before, but I'll forgive you if you can post a link to where that terminology is used. But that gate has nothing to do with XOR, and definitely has nothing to do with the quantum C-NOT gate. The whole point of quantum gates is that they are reversible, of which AND and OR (and there negative-true counterparts) are not.

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Now allow me to quote the Wikipedia article:

So you'll see how I already qualified that there is no official two-input NOT operator, it's actually a

## Re:A solid milestone... (Score:5, Interesting)

However, it is important to realise that the theory of computation had been in development since the early 1800s (and the logic underlying that had been around for centuries); by the time the first electronic devices were created, we already had a good understanding of what they could be used for, because we had been doing exactly the same things by hand for over 50 years at that point (the word "computer" originally meant a person who performed such computations, and an "electronic computer" was just a device to replicate the task that person was doing).

We can't do quantum computations by hand, so we have no real experience with the theory, and the underlying statistical methods are relatively recent developments: quantum computers do not use the classical logic that we're all familiar with. This is a massive setback compared to the development of the electronic computer - and advances in theory usually can't be accelerated all that much. It is likely to be between 50 and 100 years before we know enough to build non-trivial applications out of quantum computers. Not because we can't build the hardware, but because we don't know how to write any software to run on them. The entire field of software development will have to be reinvented, and we don't actually know that it will be useful for anything. Unlike the first electronic computers, which had very real and obvious applications performing the tasks that were currently being done by hand, we have only vague theories and ideas about what quantum computers might be useful for. (Even the much-quoted method for breaking certain encryption algorithms is based on various assumptions that aren't proven; we don't know for sure whether quantum computers will actually be able to run it, yet)

We'll get there eventually, but it will probably take a long time and we can't really predict at this stage whether it'll be particularly useful. From what we know so far, these things are going to be incredibly arcane and obtuse to work with, and that is going to make it difficult. We might see it in our lifetimes, but I wouldn't place any bets on it, it might take much longer. The things we're playing with today may turn out to be the Babbage engines of quantum computing.

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We can't do quantum computations by hand, so we have no real experience with the theory, and the underlying statistical methods are relatively recent developments: quantum computers do not use the classical logic that we're all familiar with

I'm not an expert on Quantum computers, but I think the math/computer science is WAY ahead of the physics on this one. Please correct me if I'm wrong, but I think a Quantum computer is to a normal computer as a NFA is to an DFA (http://en.wikipedia.org/wiki/Nondetermini

## Re:A solid milestone... (Score:4, Informative)

I'm not an expert on Quantum computers, but I think the math/computer science is WAY ahead of the physics on this one. Please correct me if I'm wrong, but I think a Quantum computer is to a normal computer as a NFA is to an DFA (http://en.wikipedia.org/wiki/Nondeterministic_fin ite_state_machine). In this case it's really not a new idea at a fundamental logical level.I am an expert, and I don't think CS is ahead here; rather, I'd say CS and physics are moving forward in a partnership. As best as we understand the relevant complexity classes, quantum computer are not equivalent to an NFA. To put it another way, as far as we know, quantum computers cannot efficiently solve NP-complete problems. I say "as far as we know" because we don't even know for sure whether classical computers can efficiently solve such problems. Quantum information is a fundamentally new concept to CS, however.

Similarly, conventional computers can solve the same set of problems that quantum computers can solve, they just require an expansion of the problem which in the real world requires much more time and/or space to complete.If you look simply at the domain of solvable computational problems, and don't care about efficiency, then yes, there's no difference. There are, however, communication problems and quantum "games" that cannot be solved with classical information but can be with quantum information.

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This is a massive setback compared to the development of the electronic computer - and advances in theory usually can't be accelerated all that much. It is likely to be between 50 and 100 years before we know enough to build non-trivial applications out of quantum computers. Not because we can't build the hardware, but because we don't know how to write any software to run on them.Technically it was only 40 years before the theory of relativity and the creation of its application in nuclear reactions.

Of cou

## Re:A solid milestone... (Score:4, Interesting)

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It's not an XOR. CNOT differs from XOR in the following case: input 0, control 1.

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This isn't an ordinary NOT gate, it's a controlled NOT, or C-NOT. This gate does have two inputs. The state of the first input is either inverted or not inverted, depending on the state of the second input. So it is actually very similar to a conventional XOR gate.

By all means, pull numbers out your ass on what your predictions on when you think a quantum computer will be built, but you should at least put in a disclaimer that you have no idea what you are talking about. WTF is a `quantum transitor'

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Disclaimer: I am a quantum information scientist.If you re-read the article, you'll see that the gate is a controlled-NOT (aka CNOT) gate, rather than a simple NOT gate. CNOT is a two-bit (or, in this case, two-qubit) gate. Simply being able to make and maintain single qubits is challenging (at least, for superconducting systems), manipulating single qubits is more challenging, and performing two-qubit operations is extremely hard. It's worth noting that this result is not the first example of a two-qubit

## wrong gate (Score:2)

http://en.wikipedia.org/wiki/Cnot [wikipedia.org]

## Like in Borat? (Score:3, Funny)

It's a Quantum Gate.... NOT!

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## Fuzzy qubits of unknown distinction? (Score:1)

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## They say that it works (Score:5, Funny)

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Yes. If it consists of "the same amount" 0 and 1, then it will simply not change. That's called an eigenstate of the operator. However, you might be in a superposition of 0 and 1 where you have a bit more 0 than 1, and then you'll get something which is a bit more 1 than 0.

Actually, it's still a bit more complicated than that. There are many ways to have a state which is 0 and 1 at the sa

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Fuzzy logic is, after all, all about multi-state truth values and proportions of truth. So given your description, it sounds like with this gate what can be done is to (eventually, of course) create a non-deterministic fuzzy application platform with very high speed and very small storage requirements.

Is that in the right stall, conceptually, or am I missing the barn?

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What I'm really wanting to know though, is not how it's done, but how it's to be used.

In current fuzzy systems, it's simple enough to have something that's neither 1 nor 0 until your collapse the value. It's even easy enough to not collapse a value and to do things to a certain degree when that makes sense. That's wha

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Those do exist. There's another type, though, that is a fully fuzzy system. A canonical example is a thermostat.

Instead of 99% "do it" vs 1% "don't do it" as to turning on a furnace to raise a temperature (a fuzzy to discrete system), a variable valve could be used to turn the fuel flow on to 99%, or to 3%, or 57%.

## Quantum states (Score:4, Interesting)

Someone with some understanding of this stuff please elaborate, before my head asplodes.

## Re:Quantum states (Score:5, Funny)

*ba-dum-tsch* Thank you very much, I'll be here all week.

## Re:Quantum states (Score:4, Informative)

More seriously, a qubit (short for "quantum bit") has two well defined states, 0 and 1 (|0> and |1> for those QM buffs) just as a regular (classical) bit. The difference is that the classical bit has to be in either 0 or 1, while the qubit can be in what is called a "superposition" of those. So you could have a qubit in the 0 state, or in the 1 state, or in the "x% 1 and y% 0" state (where x+y=100). Part of the magic of quantum computers comes from this fact: using the proper operations, you can feed your quantum computer a register which is set up to "all possible inputs" so that it applies the algorithm to all possible values. Some people call this "Massive parallelism". You have to be careful, because Quantum Mechanics does not allow to extract the result of all those calculations (that would be great), so you have to go through some tricks to get useful information out of that "parallel processing".

I hope this helped some!

Pablo B.

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That is almost, but not quite, entirely unrelated to quantum computing (it's got something to do with quantum physics, that's about where the relationship ends - I think it's about the chemistry of atoms). I don't believe it's true except under specific circumstances, anyway.

Quantum computers operate on qubits, which take on any state alon

## Re:Quantum states (Score:5, Informative)

The quantum states you're referring to do have something to do with this. However, their number isn't what's important.

The interesting thing about the quantum computing world is that such states can be in superposition, that is, it is unclear whether or not the state is one or the other. You can only know that if you measure the state, the outcome will be state A in, say, 30% of the time, and state B in 70%. Now, you could probably extend this to 32 different states, but since we're used to bits, we'll build something where we just use two (for instance linearly polarized photons -- 0 degrees = 0, 90 degrees = 1).

Now, there exist methods (or they're being researched) that allow you to put your bit into a superposition of its states. This could, for instance, be so that measuring the state will produce a 0 exactly half the time. Maybe you could put your Schroedinger cat in the box -- dead=0, alive=1...

This by itself is not particularly exciting. But you could do that for multiple bits (say a 32-qubit word) so that measuring it, you get uniform probability to measure any number between 0 and 4294967295. Where it really gets interesting is when you apply quantum operators to your state: They can transform the state without destroying the superposition, i.e. without measuring it. For instance, if your superposition currently gives you 30% chance for measuring a 0 and 70% for a 1, then a CNOT gate would reverse that probability.

Note, however, that a CNOT is a "controlled not": it has two inputs, the control and the target. The control passes through unchanged, but the target is flipped if and only if the control is 1 (i.e. the target output value is identical to the XOR of the input values). In a quantum world, this lets the two bits be entangled: For instance, if the target bit is 1, then the output of the target is 1 iff the control is 0 (target = NOT control). Now suppose that we create a superposition on the control input -- then the control output will be that same superposition, but the target output will be (NOT control) for all control values. In other words, we've just computed a function for all possible input values at once. And you can build these things larger, to do more useful things, such as with a 32-qubit input.

The problem is, you thus get all possible results at the same time, but it's a superposition, and after measuring, you'll only have one result. Why is this useful? Because for one, you can construct some algorithms that transform the problem in such a way as to give a guaranteed result; in other cases, you'll do multiple samples and after a while you'll get your result -- and for some problems, you'll get it orders of magnitude quicker, on average, than on classical computers.

For instance, the Deutsch-Josza algorithm is such an example. Assume I have a function that does one of two things -- it is either constant over the whole input domain, or it is balanced, that is, it returns 0 for exactly half the possible inputs and 1 for the other half. The function, to you, is a black box. How do you determine quickly whether the function is constant or balanced? On a classical computer, you have to test one more than half the inputs, in the worst case, to find out whether the function is balanced or constant. Using the Deutsch-Josza algorithm, you can solve the problem in *constant* time on a quantum computer.

In other words, quantum computing may be interesting for some number-crunching applications. Of course the true capabilities of such a system are not yet completely understood. But I would think that for desktop computing it's probably not too relevant...

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Oh, wait, you posted a link to wikipedia. Perchance, that is the limit of your knowledge on the subject as well then?

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## Cracking (Score:4, Informative)

In theory, quantum computers would allow hackers to crack today's toughest coded messages.That's an overstatement. A quantum computer will not suddendly magically crack the strongest codes. Yes, certain algorithms designed for quantum computers, like Grover's algorithm, will reduce the time needed to find the key of a symmetrical cipher with about half the number of bits in the key. However, given for example a 256-bit key you would still have ~2^128 keys to check and afaik 2^128 still takes quite sometime to crack....

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quantumcryptography.## Re: (Score:1)

oneNP-complete problem in P time, it can doallNP problems in P time?## Re: (Score:1)

Note that factoring is not known to be, and suspected (by gut feel only) to not be, NP complete.

## Quantum gates? (Score:5, Funny)

The future of the human race is up to one lone marine now. Thanks a lot, scientists.

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## In 20 (50?) years... (Score:1, Funny)

## I fear for the programmer's sanity (Score:1)

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I think its only operation was something like subtract A from B, and if negative jump to C.

However, google will probably do better than my addled memory.

## A long way off yet! (Score:2)

Well, at the current rate of progress, we might see a Quantum Pentium III in about 26-52 years, depending on whether its "next year" or "two". I might be dead of old age by then.

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## Hans Mooij of the Delft University of Technology? (Score:1, Redundant)

## Inversed qubit? (Score:2, Interesting)

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The tricky thing is, quantum mechanics won't let you measure anything other one of two values (not strictly true, but go with me on this). But those values don't necessarily have to be 0 and 1, just so long as they are orthogonal to each other.

Okay, to understand that last bit you need to bring

## Does this make D-Wave's quantum computer obsolete? (Score:1, Interesting)

(comment 2):"How come Delft U has been able to perform a CNOT with two qubits using superconducting technology? I thought Rose/D-wave claimed it was extremely difficult to do discrete quantum gates with superconducting technology. What are the present & future limitations of the Delft "quantum computer?"

Rose IGNORED the question. The quantum computer built by D-Wave [wikipedia.org] is an adiabatic computer (which is an analog computer), whereas the Delft peop

## Argh (Score:1)

## NOT Moore's Law (Score:3, Funny)

the result may pave the way for devices of double the size in the next year or twoHmm, seems like they've successfully performed a NOT on Moore's law.

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## For what purpose? (Score:1)

## Sounds familiar... (Score:2)

by turning bits into fuzzy quantum things called qubits (pronounced cue-bits) that are 0 and 1 simultaneouslySounds like any ol' woman to me, nothing to worry about, we have been handling it for centuries.

## Maybe not so great... (Score:2)

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I have no evidence of this, of course, but it's too important a problem for the experts to ignore. Lest you forget, the government too has data it seeks to keep secret, and while bas

## Wow. ? (Score:4, Funny)

## A little insight (Score:1)

## perl -qm (Score:2)

## both 0 and 1 simultaneously (Score:2)

Just because a wave function has to collapse into one eigenstate when it is

## backwards not forwards (Score:2)

After recent success in using quantum computing for superconducting qubits, researchers from Delft have formed the first Controlled NOT quantum gateHow is this a step forward, I thought we already had gates that were NOT quantum gates...

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A 'bit' is simply shorthand for "binary digit". Quantum digits, however, aren't binary, since they can represent much more than a simple 0 or 1. By adding the 'Qu-' to the term, we are essentially calling them "Quantum Binary Digits," which is in itself an oxymoron.Qubits are quantum bits in the sense that there are two basis states (often | 0 > and | 1 >). In some systems, qutrits (quantum trinary digits) are more natural, and occasionally, you'll hear "qudit", which is a d-level quantum digit, for s

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Disclaimer: I am a quantum information scientistQubits represent a probability of being a 0 or 1. Observing a qubit destroys that probability, and you "read" only a zero or a one.This is at best an incomplete description of what happens. Qubits are

quantum states, not probabilities. Quantum states are sometimes called "probability amplitudes", in that taking the square of the magnitude of the coefficient for a particular basis state gives you the probability of getting that state if you measure in that basi## Re: (Score:2, Informative)

______

-| NOT|-

-|____|-

the gate has two inputs and two outputs

in direct computation the the inputs are on the left, the outputs on the right

in reverse computation the other way around

let's take direct computation,

say the inputs(left side) are in_x(top) and in_y(bottom) and the outputs(right) out_x(top) and out_y(bottom)

the C-Not performs the following function:

out_x

out_y

BUT it performs thi