physics

Quantum Computation Language

Quantum Computation Language is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quantum Computation Language rather than just read about it. In short: Quantum Computation Language (QCL) is one of the first implemented quantum programming languages. The most important feature of QCL is the support for user-defined operators and functions.

Key takeaways

Quantum Computation Language belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Quantum Computation Language to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Quantum Computation Language from memory before moving on to harder problems.

Reference excerpt

Quantum Computation Language (QCL) is one of the first implemented quantum programming languages. The most important feature of QCL is the support for user-defined operators and functions. Its syntax resembles the syntax of the C programming language and its classical data types are similar to primitive data types in C. One can combine classical code and quantum code in the same program. The language was created before there were multi-qubit quantum computers and the only implementation of QCL uses an interpreter with a built-in classically simulated quantum computer. QCL was created to explore programming concepts for quantum computers. The QCL library provides standard quantum operators used in quantum algorithms such as:

Controlled-not with many target qubits, Hadamard operation on many qubits, Phase and controlled phase. Quantum algorithms for addition, multiplication and exponentiation with binary constants (all modulus n) The quantum fourier transform

Syntax Data types Quantum - qureg, quvoid, quconst, quscratch, qucond Classical - int, real, complex, boolean, string, vector, matrix, tensor Function types qufunct - Pseudo-classic operators. Can only change the permutation of basis states. operator - General unitary operators. Can change the amplitude. procedure - Can call measure, print, and dump inside this function. This function is non-invertible. Built-in functions Quantum qufunct - Fanout, Swap, Perm2, Perm4, Perm8, Not, CNot operator - Matrix2x2, Matrix4x4, Matrix8x8, Rot, Mix, H, CPhase, SqrtNot, X, Y, Z, S, T procedure - measure, dump, reset Classical Arithmetic - sin, cos, tan, log, sqrt, ... Complex - Re, Im, conj

Examples The basic built-in quantum data type in QCL is the qureg (quantum register). It can be interpreted as an array of qubits (quantum bits).

Since the qcl interpreter uses qlib simulation library, it is possible to observe the internal state of the quantum machine during execution of the quantum program.

Note that the dump operation is different from measurement, since it does not influence the state of the quantum machine and can be realized only using a simulator. Like in modern programming languages, it is possible to define new operations which can be used to manipulate quantum data. For example:

defines inverse about the mean operator used in Grover's algorithm (it is sometimes called Grover's diffusion operator). This allows one to define algorithms on a higher level of abstraction and extend the library of functions available for programmers.

References

Worked examples

Example 1 — a first encounter with Quantum Computation Language

Start with the simplest possible case. Write down what Quantum Computation Language claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quantum Computation Language before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quantum Computation Language ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quantum Computation Language

In research: Quantum Computation Language appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quantum Computation Language in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quantum Computation Language is common in secondary-school and first-year university syllabi. It links to neighbouring topics Programming languages, Quantum programming, so understanding it makes those chapters shorter.
In everyday life: Look for Quantum Computation Language outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quantum Computation Language in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quantum Computation Language means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quantum Computation Language out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quantum Computation Language in simple terms?

Quantum Computation Language (QCL) is one of the first implemented quantum programming languages. The most important feature of QCL is the support for user-defined operators and functions.

Why does Quantum Computation Language matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quantum Computation Language?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quantum Computation Language.