What is a Qubit? - A Beginner's Guide to Quantum Computing

the bid is the most basic unit of information in classical Computing and classical information in Quantum computation and Quantum information a Quantum bit or qubit plays a similar role in this video we will see what the qubit actually means and compare its properties to those of classical bits we're going to describe qubits as mathematical objects with certain specific properties it is true that qubits like bits are realized as actual physical systems the beauty of treating qubits as abstract entities allow scientists to construct a general theory of quantum computation and Quantum information independent of any particular physical system what is then a cubit just as a classical bit has a state either zero or One A qubit also has a state two possible States for a qubit are the state's KET 0 and Cat one which are similar to the states zero and one of a classical bid this weird notation is called the Dirac notation and is a standard notation for representing a state in quantum mechanics the difference between bits and qubits is that unlike bits qubits can be in a state other than cat0 or cat 1. it is perfectly legal to have a linear combination of these two states this phenomenon is called Quantum superposition the numbers Alpha and beta are in general complex numbers the special States cat0 and ket1 are known as computational base Estates and form an orthonormal basis for this Vector space let's now explore the fundamental difference between a bit and a qubit it is always possible to examine a bit to determine if it is in state 0 or 1. for example computers do this all the time when they retrieve the contents of their memory rather remarkably it is not possible to examine a qubit to determine its Quantum state for learning the quantum state of a qubit we need to learn the values of Alpha and beta however quantum mechanics tell us that we can only acquire much more restricted information about the quantum state when we measure a qubit we get either the result cat 0 with probability Alpha squared or the result ket1 with probability beta squared so from a single measurement we will not be able to learn the values of both Alpha and beta thus in general a qubit state is a unit Vector in a two-dimensional complex Vector space and measurement collapses it into one of the bases qubit's ability to be in superposition States runs counter to our common sense a classical bit is like a coin either heads or tails up by contrast a qubit can exist in a Continuum of States between cat0 and Cat 1 until it is observed let us emphasize again that when a qubit is measured it only ever gives zero or one as the measurement result probabilistically for example a qubit can be in the state which when measured gives the result zero fifty percent of the time and the result one fifty percent of the time this state which is in an equal superposition of KET 0 and Cat 1 is quite an important Quantum State and is sometimes denoted by cat plus although qubits seems strange they are in fact real experiments extensively validate their existence and behavior and they can be realized using a wide range of physical systems in order to get a sense of how a qubit can be realized let's see some of the ways it can occur as the two different polarizations of a photon as the alignment of a nuclear spin in a uniform magnetic field as two states of an electron orbiting a single atom in the atom model the electron can exist in either the so-called ground or excited states which we'll refer to as cat0 and Ketone respectively by Shining Light on the atom with appropriate energy and for an appropriate length of time it is possible to move the electron from the cad0 state to the ket1 state and vice versa but more interestingly by reducing the time we Shine the Light an electron initially in the state of ked0 can be moved halfway between cat0 and Cat 1 into the KET plus State historically a great deal of attention has been given to the meaning or interpretation that might be attached to superposition States and to the inherently probabilistic nature of observations on Quantum systems however for almost all practical purposes related to Quantum information processing it is not necessary to concern with such discussions how much information is represented by a qubit paradoxically we can do infinite binary expansion of values Alpha and beta so in principle it could store infinite information however this conclusion turns out to be misleading because of the behavior of a qubit when observed recall that measurement of a qubit will give only either zero or one furthermore measurement changes the state of a qubit collapsing it from its superposition of cad0 and Cat 1 to the specific State consistent with the measurement result for example if the measurement of cat plus gives zero then the state of the qubit after measurement will be cat0 why does this type of collapse occur nobody knows until now we simply accept it as a law of Nature and include it as one of the fundamental postulates of quantum mechanics what is relevant for our purposes is that from a single measurement one obtains only a single bit of information about the state of the qubit thus resolving the apparent paradox nevertheless there is something conceptually important going on here when Nature performs an operation on a closed Quantum system of qubits without performing any measurement she does keep track of all the infinite parameters of Alpha and beta even though that information is hidden from us nature conceals a great deal of hidden information and even more interestingly the potential amount of this extra information grows exponentially with the number of kids understanding this hidden Quantum information lies at the heart of what makes quantum mechanics a powerful tool for information processing and the future of computation in this video we focused on what a qubit means what we can do with it and what we count furthermore much of the discussion was on a single qubit in the coming videos we will explain what happens if we have more than one qubit spoiler alert entanglement foreign [Music]

Channel: Quantverse

Views: 10,462

Keywords: qubits, quantum computing, bit, bit vs qubit, quantum computing explained, quantum physics explained, quantum physics, quantum computer

Id: 90za6mazNps

Length: 7min 11sec (431 seconds)

Published: Sat Jan 07 2023