{"id":2098,"date":"2026-04-07T09:50:26","date_gmt":"2026-04-07T07:50:26","guid":{"rendered":"https:\/\/www.milq.info\/?page_id=2098"},"modified":"2026-04-07T11:52:38","modified_gmt":"2026-04-07T09:52:38","slug":"glossary","status":"publish","type":"page","link":"https:\/\/www.milq.info\/en\/qti\/basics\/glossary\/","title":{"rendered":"Glossary"},"content":{"rendered":"
<\/div>

<\/p>\n

Terms<\/h1>\n

Basic rule 1 (statistic)<\/a> – Basic rule 2 (interference)<\/a> – Basic rule 3 (measurement)<\/a> – Basic rule 4 (complementarity)<\/a> – Basic rule 5 (entanglement)<\/a> – Beam splitter<\/a> – Complementarity<\/a> – Emission<\/a> – Entanglement<\/a> – Ensemble<\/a> – Hadamard gate<\/a>\u00a0 – Interference<\/a> – Measurement<\/a> – No-cloning theorem<\/a> – Particlelike<\/a> – Phase shifter<\/a> – Polarisation<\/a> – Preparation<\/a> – Pseudo-random number generator<\/a> – Qubit<\/a> – Quantised<\/a> – Quantum random number generator<\/a> – Reflection<\/a> – Repeater<\/a> – Transmission<\/a> – True random number generator<\/a> – Superposition<\/a> – Wavelike<\/a> – Wave-particle dualism<\/a><\/p>\n

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Explanations<\/h1>\n
\n

Basic Rule 1 (Statistical Behavior):<\/strong><\/h2>\n

Single events are not predictable, they are random. Only statistical predictions (for many repetitions) are possible in quantum physics.<\/p>\n

\n

Basic Rule 2 (Interference of single quantum objects):<\/strong><\/h2>\n

Interference occurs if there are two or more \u201cpaths\u201c leading to the same experimental result. Even if these alternatives are mutually exclusive in classical physics, none of them will be \u201crealised\u201c in a classical sense.<\/p>\n

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Basic Rule 3 (Definite Measurement Results):<\/strong><\/h2>\n

Even if quantum objects in a superposition state need not have a fixed value of the measured quantity, one always finds a definite result upon measurement.<\/p>\n

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Basic Rule 4 (Complementarity):<\/strong><\/h2>\n

There are pairs of observables that cannot be simultaneously prepared to certain values on an ensemble of quantum objects.<\/p>\n

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Basic Rule 5 (Entanglement): <\/strong><\/h2>\n

Multiple quantum objects can be entangled and be related in a very particular way regardless of spatial position. Entangled quantum objects cannot be described as individual uncorrelated systems.<\/p>\n

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Beam Splitter:<\/strong><\/h2>\n

A beam splitter is a device used to split incoming beams. It is often a semi-transparent mirror, which allows beams to pass through as well as being reflected. In the context of the videos and learning material, we mostly use\/demonstrate beam splitters that have a 50\/50 reflection\/transmission ratio. Other splittings are possible, such as 60\/40.<\/p>\n

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Complementarity:<\/strong><\/h2>\n

In quantum physics, complementarity describes two observables or properties of an object that cannot exist simultaneously. Important examples of complementarity are wave-particle duality, Heisenberg’s uncertainty principle or the polarisation of light. In all these cases there are two aspects that cannot exist or be defined at the same time. Within the learning material, we focus on preparing a pair of observables simultaneously. This is not possible for specific pairs of observables, like for example position \u2013 momentum and H\/V \u2013 +\/-. The preparation of one observable leads to a random measurement result regarding the other, complementary observable. If the measurement would not be random, this would mean that the quantum object has been prepared regarding this observable. But this is not possible due to the principle of complementarity.<\/p>\n

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Emission:<\/strong><\/h2>\n

The word emission is of Latin origin and is divided into “ex” – “out” and “mittere” – “to send”. In this context, it is used to describe the fact that light is sent out from an object.<\/p>\n

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Entanglement:<\/strong><\/h2>\n

Entanglement is an interesting phenomenon that can be observed and induced in quantum objects. The point is that several quantum objects no longer act independently of each other, they cannot be described as individual uncorrelated systems anymore. The measurement result of one quantum object is directly reflected by the other entangled quantum object and an (anti-)correlation of the measurement results can be observed.<\/p>\n

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Ensemble:<\/strong><\/h2>\n

An ensemble is a multitude of quantum objects that are brought into the same state by an experimental arrangement.<\/p>\n

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Hadamard gate:<\/strong><\/h2>\n

The Hadamard gate is an example of a quantum gate. It is able to transfer qubits in superposition states of 0 and 1. You can see the mathematical description of a Hadamard gate in the image below; it means that the wave function of a qubit is transferred from a certain state to a superposition state.<\/p>\n

\"H = \frac{\ket{0} + \ket{1}}{\sqrt{2}}\bra{0} + \frac{\ket{0} - \ket{1}}{\sqrt{2}}\bra{1}\"<\/p>\n

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Interference:<\/strong><\/h2>\n

Interference is a phenomenon that is not only observable in quantum physics or with quantum objects. It can also be observed in classical optics, for example in experiments with interferometers. Interference is caused by the superposition of waves, resulting in an addition of the waves. Two important phenomena can be observed: constructive and destructive interference. Constructive interference<\/strong> occurs when two wave maxima or two wave minima meet. In this case, the waves overlap in such a way that the resulting wave has larger amplitudes. If both waves overlap in such a way that the wave maxima and wave minima overlap, the resulting wave ends up with reduced amplitudes. This is called destructive interference<\/strong>.<\/p>\n

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Measurement:<\/strong><\/h2>\n

In quantum physics, measurement is an active process. In contrast, in classical physics, measurement is the finding of an already determined property. A measurement is made when a quantum system interacts with its environment, leaving information about its state, position or other properties. Such an interaction leads to the cancellation of superposition and, if present, of interference.<\/p>\n

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No-cloning theorem:<\/strong><\/h2>\n

The no-cloning theorem states that a quantum object cannot be cloned. It is not possible to have an exact copy of a quantum object and its states.<\/p>\n

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Particlelike:<\/strong><\/h2>\n

Quantum objects are measured particlelike. The result is definite and the quantum object behaves like a particle.<\/p>\n

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Phase Shifter:<\/strong><\/h2>\n

The phase shifter is a component of the presented structure for using interference. It shifts the phase of the qubit. Mathematically it can be described as the state 0 being transferred to itself or the state 1 being shifted by \"\varphi\" .<\/p>\n

\"P(\varphi) = \begin{bmatrix} 1&0\\0&e^{i\varphi}\\ \end{bmatrix}\"<\/p>\n

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Polarisation:<\/strong><\/h2>\n

Polarisation is a property of waves, and since we can describe light (and analogous single photons) as waves, it is indeed a property of light. Polarisation describes the direction of wave oscillation. Most of the light we see in our daily lives is unpolarised, meaning that it has no definite polarisation, but is a superposition of parts of light with different polarisations. You can get linear polarised light by using a polarisation filter.<\/p>\n

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Preparation<\/strong>:<\/h2>\n

Preparation is a procedure by which (quantum) objects are brought into a desired state and defined to certain values. Certain properties are attributed to the (quantum) object by the preparation process. This can be verified through measurements of the (quantum) objects.<\/p>\n

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Pseudo-Random Number Generators:<\/strong><\/h2>\n

Pseudo-RNGs are mathematical algorithms that generate random-like numbers. The numbers appear random but are actually deterministic and based on deterministic algorithms. These algorithms work with given “random” seeds, which are taken from various sources such as mouse movements, dates or time.<\/p>\n

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Qubit:<\/strong><\/h2>\n

The Qubit is the basic building block of a quantum computer. Analogous to a classical bit, the qubit is also divided into 0 and 1. Unlike classical bits, qubits can be in a state of superposition, existing simultaneously in both states 0 and 1.<\/p>\n

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Quantised:<\/strong><\/h2>\n

For an object to be quantised means that it has a discrete structure rather than a continuous one. In terms of light, this means that light is made up of many photons that are discrete\/consist of packets of energy. The discrete nature of these can be seen in the anticoincidence experiment, as there is only one detection at a time.<\/p>\n

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Quantum Random Number Generator:<\/strong><\/h2>\n

Quantum RNGs take their random numbers from quantum processes. These are random and not predictable or calculable because quantum physics, or individual events of quantum physics, are truly random and indeterministic.<\/p>\n

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Reflection:<\/strong><\/h2>\n

The beam splitter is positioned at an angle of 45\u00b0 so that the reflected part of the light can also be used. Reflection means that something is thrown back, in this case light thrown back by the beam splitter. The word is of Latin origin.<\/p>\n

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Repeater:<\/strong><\/h2>\n

The purpose of a repeater is to amplify an existing signal. It is therefore most often used in the context of communications, where signals above a certain distance are no longer strong enough and therefore need to be continuously amplified. In the context of classical physics, this is perfectly feasible. In quantum physics, however, the no-cloning theorem is a limitation. Quantum objects cannot be “simply” amplified or cloned. For this reason, a new concept of repeaters is required, which in the case of quantum physics makes use of entangled photons.<\/p>\n

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Transmission:<\/strong><\/h2>\n

The word transmission has a Latin origin and is divided into “trans” – “through” and “mittere” – “to send”. In this context it describes light passing through an object.<\/p>\n

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True Random Number Generator:<\/strong><\/h2>\n

True-RNGs derive their random numbers from classical physical processes that are theoretically predictable and calculable. In practice, the numbers are unpredictable and non-computable because they have too many unknown variables, degrees of freedom, or depend on a system with chaotic behaviour.<\/p>\n

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Superposition:<\/strong><\/h2>\n

Quantum objects can be in a superposition state. It is possible for them to exist in different states at the same time without realising the states in a classical way.<\/p>\n

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Wavelike:<\/strong><\/h2>\n

Quantum objects also behave like waves, especially when they are not measured. Here they show wavelike properties, such that for example interference can occur.<\/p>\n

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Wave-Particle Dualism:<\/strong><\/h2>\n

Quantum objects can be described as both, wavelike and particlelike. Their behaviour changes depending on their current situation. In most cases, the rule of thumb is that they spread like waves and are measured like particles. This means that when not measured, the quantum object behaves like a wave and can also be described mathematically by a wave function. When measured, the quantum object behaves like a particle, with a definite state, position, momentum or other characteristic. The measurement is definite and clear.<\/p>","protected":false},"excerpt":{"rendered":"

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