5 ms·

In classical computing, a bit is a binary state. The implementation isn't important. What is important is there are only two positions: true/false, on/off, el

In classical computing, a bit is a binary state. The implementation isn't important. What is important is there are only two positions: true/false, on/off, electricity flowing/no electricity flowing, a wooden stick pointed to the left/right. If you treat combinations of state as binary numbers (0000=0, 0001=1, 0010=2, 0011=3, etc) and you create functions that manipulate these bits (AND, OR, NOT, etc gates) such that they generate new patterns of bits consistent with doing math. A classical computer relies on classical physics: something exactly is something. You either have a 1 or 0, because the implementation is either one thing or the other thing. Quantum computing relies on quantum effects, say the spin of an electron. The spin of the electron can be measured and when does it will either be up or down. At first it seems like it's just like a classical computer; however, it's possible to "entangle" multiple qbits together. The orientation becomes fuzzy. In this fuzzy state is possible to create quantum gates that again do math, but these results become "fuzzy." So I create the function: "Give x such that x has the reminder of 1 after dividing by some huge number?" In classical physics there is no one answer to modulus. There could be an infinite number of possible answers. Solving it with a classical computer does not mean much more than trying values and seeing what works. But, asking that question with a quantum computer does something different. Being "fuzzy," it exists across all possible states at the same time until you measure it. When you measure it, you will get a random answer but that answer will work for the equation. Say you ask the question, "Give me x where x divided by 5 has a remainder of 1." The quantum computer might first spit out 56 then next time 91 then next time 6.

Symmetry 7y ago
Your answer is a good one for helping to understand the problem and is true of almost all computers in active use today. But I want to point out that you can have a classical computer that isn't binary. Analog computers have a long history and are still used in some places today. Also ternary computers where bits can be 1, 0, or -1 had a role in Soviet computing and let you used Balanced Ternary[1] which is even nicer than Two's Complement. But these are classical in the sense of having one particular value in the way the rest of your answer lays out nicely. [1]https://en.wikipedia.org/wiki/Balanced_ternary https://en.wikipedia.org/wiki/Balanced_ternary
- deleted 7y ago
  [deleted]
thaumasiotes 7y ago
> however, it's possible to "entangle" multiple qbits together. The orientation becomes fuzzy. In this fuzzy state is possible to create quantum gates that again do math, but these results become "fuzzy." The fuzzy results, in my understanding, are a property of quantum mechanics and don't require multiple qubits. A single electron has some probability of spinning up and a complementary probability of spinning down, and until you go ahead and measure the spin, the actual spin value hasn't coalesced to either of those states, instead being some fuzzy intermediate probability spectrum. Entangling multiple particles means (again, as far as I understand) that their measurements cease to be independent -- if I have several pairs of entangled electrons all with spin of 50% up / 50% down, then I might expect the results of measuring the spin of those pairs to look something like this table: +/+ 25% +/- 25% -/+ 25% -/- 25% when in fact, because these are entangled pairs, I will either get +/+ 50% +/- 0 -/+ 0 -/- 50% or +/+ 0 +/- 50% -/+ 50% -/- 0 What am I missing here?
- thethirdone 7y ago
  > What am I missing here? I am unsure what you are missing because what you explained is approximately correct. Minor correction: Entangled qubits (each of 50% propbaility to be up) can have more possible measurement distributions that the two you mentioned. Distributions like the following exist. +/+ 20% +/- 30% -/+ 30% -/- 20% > if I have several pairs of entangled electrons all with spin of 50% up / 50% down, then I might expect the results of measuring the spin of those pairs to look something like this table: I think you may misunderstand how to get qubits entangled. You would have to pass two qubits through a two-qubit gate to get them entangled. And doing so would leave you with only one measurement distribution. For example if you have a qubit in 50% |1>, 50% |0> and pass it through CNOT with a qubit in |1>. You get: |11> 0 |10> 50% |01> 50% |00> 0 But if the second qubit was in state |0>, you get |11> 50% |10> 0 |01> 0 |00> 50% > if I have several pairs of entangled electrons all with spin of 50% up / 50% down Also just in case you don't know qubits have phase so there is more than one way to have a qubit that when measured will be up 50% of the time.
- cdumler 7y ago

Symmetry 7y ago

Your answer is a good one for helping to understand the problem and is true of almost all computers in active use today. But I want to point out that you can have a classical computer that isn't binary. Analog computers have a long history and are still used in some places today. Also ternary computers where bits can be 1, 0, or -1 had a role in Soviet computing and let you used Balanced Ternary[1] which is even nicer than Two's Complement. But these are classical in the sense of having one particular value in the way the rest of your answer lays out nicely. [1]https://en.wikipedia.org/wiki/Balanced_ternary https://en.wikipedia.org/wiki/Balanced_ternary

deleted 7y ago
[deleted]

thaumasiotes 7y ago

> however, it's possible to "entangle" multiple qbits together. The orientation becomes fuzzy. In this fuzzy state is possible to create quantum gates that again do math, but these results become "fuzzy." The fuzzy results, in my understanding, are a property of quantum mechanics and don't require multiple qubits. A single electron has some probability of spinning up and a complementary probability of spinning down, and until you go ahead and measure the spin, the actual spin value hasn't coalesced to either of those states, instead being some fuzzy intermediate probability spectrum. Entangling multiple particles means (again, as far as I understand) that their measurements cease to be independent -- if I have several pairs of entangled electrons all with spin of 50% up / 50% down, then I might expect the results of measuring the spin of those pairs to look something like this table: +/+ 25% +/- 25% -/+ 25% -/- 25% when in fact, because these are entangled pairs, I will either get +/+ 50% +/- 0 -/+ 0 -/- 50% or +/+ 0 +/- 50% -/+ 50% -/- 0 What am I missing here?

thethirdone 7y ago
> What am I missing here? I am unsure what you are missing because what you explained is approximately correct. Minor correction: Entangled qubits (each of 50% propbaility to be up) can have more possible measurement distributions that the two you mentioned. Distributions like the following exist. +/+ 20% +/- 30% -/+ 30% -/- 20% > if I have several pairs of entangled electrons all with spin of 50% up / 50% down, then I might expect the results of measuring the spin of those pairs to look something like this table: I think you may misunderstand how to get qubits entangled. You would have to pass two qubits through a two-qubit gate to get them entangled. And doing so would leave you with only one measurement distribution. For example if you have a qubit in 50% |1>, 50% |0> and pass it through CNOT with a qubit in |1>. You get: |11> 0 |10> 50% |01> 50% |00> 0 But if the second qubit was in state |0>, you get |11> 50% |10> 0 |01> 0 |00> 50% > if I have several pairs of entangled electrons all with spin of 50% up / 50% down Also just in case you don't know qubits have phase so there is more than one way to have a qubit that when measured will be up 50% of the time.
cdumler 7y ago