Qubits are in a superposition which means that they can currently be both digits of 1 and 0 at the same time BUT this is my question:  If Qubits have to be filtered to be used then what makes them better than normal bits after they are filtered? they are going to become 1 OR 0 because they can't be used in their superposition (If I'm correct), so the way I see it they are just normal bits we just have to take the extra time to filter first. It would be much more efficient (the way I see it) to simply re-arrange bits (like 1001 to 1100 or 1010 they use the same bits but get multiple results) to get faster results ya-know?  So if someone could tell me why quantum computing is so much better I would appreciate it a lot! If I said anything wrong than please correct me!
122924
Classical computers store information in bits, which can either be $0$ or $1$, but, in a quantum computer, the qubit can store $0$, $1$ or a state that is the superposition of these two states. Now, when we make a "measurement" (to determine the state of qubit), it changes the state of the qubit, collapsing it from its superposition of $0$ and $1$ to the specific state consistent with the measurement result.  If from a measurement of a qubit we obtain only a single bit of information ($0$ or $1$, because the qubit collapses to either of the states), then, how is a qubit better than a classical bit? Since ultimately we are only able to get either $0$ or $1$ from either classical or quantum bit.  If you can explain with an example, it may be helpful.
68703
I've always hit two big stumbling blocks in conceiving of the proof or disproof of  as being even valid idea, let alone an answerable question... I feel I must be misunderstanding some very fundamental things.   Quantum mechanics is deterministic, ignoring the bit where we take our complex number and fudge it into a probability. We use computers to make calculations to provide the predictions of quantum mechanics - how is this not itself a hidden variable theory?   From what I understand the famous Bell theorem and work around it doesn't disprove hidden variable theories, just one specific flavour of them, and even then I am not convinced. I feel like I must be missing something again, because this result seems to me in no way profound... although it certainly fits into the picture of the EPR 'paradox' and is a good demonstration of the validity of QM.  I guess the crux of my problem is that this 'area' really addresses wave function collapse and the problems it causes, but I don't see the need for some collapse mechanism to begin with... again I feel like I am missing something really fundamental.  Apologies if this is a bad question. I have had a look around and there are similar questions, but I don't feel that either of my points are addressed...
22733
It seems that quantum computing is often taken to mean the quantum circuit method of computation, where a register of qubits is acted on by a circuit of quantum gates and measured at the output (and possibly at some intermediate steps). Quantum annealing at least seems to be an altogether different method to computing with quantum resources1, as it does not involve quantum gates.  What different models of quantum computation are there? What makes them different?  To clarify, I am not asking what different physical implementations qubits have, I mean the description of different ideas of how to compute outputs from inputs2 using quantum resources.     1. Anything that is inherently non-classical, like entanglement and coherence. 2. A process which transforms the inputs (such as qubits) to outputs (results of the computation).
25638
I was very inspired by Michio Kaku's  on the possibilities of quantum computing and also listening to Talia Gershon's  on it.   As I come from a business &amp; analytics background, what materials can I begin exploring to prepare to learn more about the field of quantum computing? Eg. what would I need to study to understand Peter Shor's algorithm,  on physics, etc.
55962
I apologize if this is a really silly question.   In the (textbook) quantum teleportation algorithm, in the step right after Alice has measured her system but before she has sent her classical information to Bob, she is about to send one of the following values: 00,01,10,11.   What if Bob doesn't want to wait and simply takes a guess? Wouldn't there then be superluminal communication 25% of the time?
56669
So I've been reading a bit and watching some videos about the double slit experiment, and therefore the wave particle duality; I've also read this "implies" that a particle can be in two places at the same time. Can you clarify this, and how could that be possible?
15459
What ever happened to  in entangled quantum states, i.e. the ? I thought they argued that in principle one could communicate faster than speed of light with entangled, separated states when one wave function gets collapsed. I imagine this paradox has been resolved, but I don't know the reference.
96624
Can qubit be inside Bloch Sphere, i.e. its length is less than 1? If yes, how we represent that state since we have only parameter for angles and not the length (norm) of the vector?
52145
I think I roughly understand how the RSA alorithm is working.  However, I don't understand why we need the $N$, which we use as a modulus, to be $pq$ for some large primes $p, q$.  I vaguely know it has something to do with factorization, but I am kind of lost. So, hypothetical questions.   What would happen if the $N$ was not $pq$, but just a big prime? What if $N$ would be some random composite (that's easy to factor)?   The other parts of RSA would stay the same.
21176
When expressing computations in terms of a quantum circuit, one makes use of gates, that is, (typically) unitary evolutions.  In some sense, these are rather mysterious objects, in that they perform "magic" discrete operations on the states. They are essentially black boxes, whose inner workings are not often dealt with while studying quantum algorithms. However, that is not how quantum mechanics works: states evolve in a continuous fashion following Schrödinger's equation.  In other words, when talking about quantum gates and operations, one neglects the dynamic (that is, the Hamiltonian) realising said evolution, which is how the gates are actually implemented in experimental architectures.  One method is to decompose the gate in terms of elementary (in a given experimental architecture) ones. Is this the only way? What about such "elementary" gates? How are the dynamics implementing those typically found?
105820
So, 2 days ago I learned that quantum entanglement is just about our perception. There is not an active link between particles and they are not communicating with each other. But then, while surfing on the internet this page came up   It says: ""If I jiggle one electron, the other electron 'senses' this vibration instantly, faster than the speed of light. Einstein thought that this therefore disproved the quantum theory, since nothing can go faster than light," Kaku wrote."  and then I read about EPR paradox and really confused. If there is not an active link between quantum particles what Kaku is talking about ? Can someone explain?
5907
What's an atomic superstate/, and how is it possible?  I understand the basics - being something can be moving and staying still at the same time; the observer changes the behaviour - but I'd like to know a little more, as it interests me, and how is it possible without actually interfering with said thing?
78424
In the  or  there's a plenty of information about hash-based signatures. But where are hash-based ecryption with pubkey?     But, over the long-term, it's generally confidentiality (i.e. encryption) that you need to maintain and I haven't talked about post-quantum encryption at all in this post. (Maybe in the future.)   Why articles about hash-based asymmetric encryption are more hard to come by?  Possible reasons:   It is impossible and the proof is basic enough that it not deserves an article (or a question here) It is even more impractical than hash-based signatures It is secret and classified It is somehow not interesting and nobody cared to research it It is called by some other term, using which articles get found easily. Linked articles actually do speak about them, but I don't read attentively and missed it.
73853
I am very new to quantum computing and just try to understand things from a computer scientist's perspective.  In terms of computational power, what I have understood,      100 ideal qubits ...  to [$2^n$ pieces of information]   Now Rigetti Computing has  a 128 qubit computer.   Let's imagine they indeed release it next year.  This leads me to the following thoughts, please correct me if I am wrong:   let's say hypothetically due to the noise about 28 qubits can't be taken into consideration (as used for the fault tolerance for example) that is, we could work with 100 qubits as in the example above.   Could we say then, we have an analog of  i.e. say  64 qubits go for memory and 32 qubits for the instruction set (say remaining 4 are reserved).  Does this mean then (oversimplified!):   we get 2^32 bits equivalent ~ 537 MB worth of "register bits" for CPU instructions, altogether with caches (no idea who might need that but could probably become a many-core "die" see for example ), compared to say 512KB=2^15 bits cache for one level on a classical computer and for "RAM", we get remaining 2^64 bits equivalent = 2.3 exabytes worth memory? (way more than current supercomputers have; Google had though  total disk storage of 10 exabytes in 2013)
32837
int temp = 0x5E; // in binary 0b1011110.   Is there such a way to check if bit 3 in temp is 1 or 0 without bit shifting and masking.  Just want to know if there is some built in function for this, or am I forced to write one myself.
114896
I was thinking about the many interpretations of quantum physics, and one thing that never made sense to me was the many world's interpretation. Basically at any given moment for which something exists in a superposition, isn't this interpretation basically saying that there would have to exist a new universe for every possible discrete outcome that could result once the measurement is made?   So let's say an electron's location is a superposition of two distinct locations. Doesn't that mean there would at that moment have to be two distinct universes for each distinct location that is superposed? If so, then clearly the amount of universes being spawned every moment must be astronomical.   There could be trillions upon trillions of electrons(for instance) having superposed states, and then every moment in time (I suppose every planck time?), it seems there would have to be yet another set of universes spawning for every superposition.  How could this be? Surely there must be some kind of thermodynamic cost to replicate an entire universe. What would fuel or supply the additional mass and energy for every universe at every moment for every superposed state?  To my lay person's mind, this seems to be a very big weakness of this interpretation, but I needed to ask people with the physics background required to answer this question. Could there be some kind of loophole that could allow alternate universes to spawn so rapidly? Otherwise, doesn't this present a bit of a problem for taking this interpretation seriously?
768
I'm someone who writes code just for fun and haven't really delved into it in either an academic or professional setting, so stuff like these bitwise operators really escapes me.  I was reading an article about JavaScript, which apparently supports bitwise operations. I keep seeing this operation mentioned in places, and I've tried reading about to figure out what exactly it is, but I just don't seem to get it at all. So what are they? Clear examples would be great! :D  Just a few more questions - what are some practical applications of bitwise operations? When might you use them?