What is Qubits: Definition and 57 Discussions

In quantum computing, a qubit () or quantum bit (sometimes qbit) is the basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device. A qubit is a two-state (or two-level) quantum-mechanical system, one of the simplest quantum systems displaying the peculiarity of quantum mechanics. Examples include the spin of the electron in which the two levels can be taken as spin up and spin down; or the polarization of a single photon in which the two states can be taken to be the vertical polarization and the horizontal polarization. In a classical system, a bit would have to be in one state or the other. However, quantum mechanics allows the qubit to be in a coherent superposition of both states simultaneously, a property that is fundamental to quantum mechanics and quantum computing.

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    Best possible test which differentiates qubits

    What is the best possible test for differentiating qubits? Assuming we have only ONE copy of each. What if a few (but still small number of) copies were allowed?
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    What happens to qubits if Swap Test fails?

    A swap-test is described here http://en.wikipedia.org/wiki/Quantum_digital_signature#Public_Key_should_be_the_same_for_every_recipient_.28Swap_Test.29 Now if the target qubits are identical, then after the swap test they are not disturbed. But what happens to them if they weren't identical...
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    Distinguish Orthogonal Qubits: Test & Impact

    Given two arbitrary qubits, is there a test I can do that will always tell orthogonal qubits apart (but may fail if they are not)? Does it necessarily destroy the qubits' states?
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    What is density matrix of one on two entangled qubits?

    Let we have two qubits A and B. First qubit has eigenstates |A0> and |A1>, and second has |B0> and |B1>. Let them be in the entangled state, described with vector c1 * |A0> * |B0> + c2 * |B0> * |B1>| where c1 and c2 are complex numbers with |c1|^2 + |c2|^2 = 1. Then what is density...
  5. T

    Qubits Probability: Calculating Pr for State Psi 01

    Homework Statement http://img249.imageshack.us/img249/4476/46715318ov5.jpg The Attempt at a Solution I know to calculate the pr we square the number in front of the state. e.g) for state psi 00, the pr is (1/root(2))^2 But for state psi 01, do I include the imaginary number part...
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    Exploring the Basics of Qubits: Questions and Answers

    Hello everyone, Could someone explain the basics of the qubit particularly pertaining to quantum computing? Maybe if you know any good links that explain the basics or if you could explain it yourselves. I appreciate it a bunch! Thanks guys!
  7. marlon

    Mechanical Qubits: Exploring Franco Nori's Research

    Anybody read the Scientific American article on them socalled mechanical qubits ? This idea is like this : suppose you have a rope of 10cm long, when you press is together at both ends it will bend towards the right and left side. Now, if you replace this rope by a nanotube of a few...
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