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physics

Transmon

Transmon 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 Transmon rather than just read about it. In short: In quantum computing, and more specifically in superconducting quantum computing, a transmon is a type of superconducting charge qubit designed to have reduced sensitivity to charge noise. The transmon was developed by Jens Koch, Terri M.

Transmon — main illustration
Transmon — illustration

Key takeaways

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

Reference excerpt

In quantum computing, and more specifically in superconducting quantum computing, a transmon is a type of superconducting charge qubit designed to have reduced sensitivity to charge noise. The transmon was developed by Jens Koch, Terri M. Yu, Jay Gambetta, Andrew Houck, David Schuster, Johannes Majer, Alexandre Blais, Michel Devoret, Steven M. Girvin, and Robert J. Schoelkopf at Yale University and Université de Sherbrooke in 2007. Its name is an abbreviation of the term transmission line shunted plasma oscillation qubit; one which consists of a Cooper-pair box "where the two superconductors are also [capacitively] shunted in order to decrease the sensitivity to charge noise, while maintaining a sufficient anharmonicity for selective qubit control".

The transmon achieves its reduced sensitivity to charge noise by significantly increasing the ratio of the Josephson energy to the charging energy. This is accomplished through the use of a large shunting capacitor. The result is energy level spacings that are approximately independent of offset charge. Planar on-chip transmon qubits have T1 coherence times approximately 30 μs to 40 μs. Recent work has shown significantly improved T1 times as long as 95 μs by replacing the superconducting transmission line cavity with a three-dimensional superconducting cavity, and by replacing niobium with tantalum in the transmon device, T1 is further improved up to 0.3 ms. These results demonstrate that previous T1 times were not limited by Josephson junction losses. Understanding the fundamental limits on the coherence time in superconducting qubits such as the transmon is an active area of research.

… excerpt ends here. Continue reading the full article.

Illustrations

Transmon: Eigenenergies E m {\displaystyle E_{m}} (first three levels, m = 0 , 1 , 2 {\displaystyle m=0,1,2} ) of the qubit Hamiltonian as a function of the effective offset charge n g {\displaystyle n_{g}} for different ratios E J / E c {\displaystyle E_{J}/E_{c}} . Energies are given in units of the transition energy E 01 {\displaystyle E_{01}} , evaluated at the degeneracy point n g = 0.5 {\displaystyle n_{g}=0.5} . The zero point of energy is chosen as the bottom of the m = 0 {\displaystyle m=0} level. The charge qubit (small E J / E c {\displaystyle E_{J}/E_{c}} , top) is normally operated at the n g = 0.5 {\displaystyle n_{g}=0.5} "sweet spot" where fluctuations cause less energy shift and the anharmonicity is maximal. Transmon (large E J / E c {\displaystyle E_{J}/E_{c}} , bottom) energy levels are insensitive to fluctuations but the anharmonicity is reduced.
Eigenenergies E m {\displaystyle E_{m}} (first three levels, m = 0 , 1 , 2 {\displaystyle m=0,1,2} ) of the qubit Hamiltonian as a function of the effective offset charge n g {\displaystyle n_{g}} for different ratios E J / E c {\displaystyle E_{J}/E_{c}} . Energies are given in units of the transition energy E 01 {\displaystyle E_{01}} , evaluated at the degeneracy point n g = 0.5 {\displaystyle n_{g}=0.5} . The zero point of energy is chosen as the bottom of the m = 0 {\displaystyle m=0} level. The charge qubit (small E J / E c {\displaystyle E_{J}/E_{c}} , top) is normally operated at the n g = 0.5 {\displaystyle n_{g}=0.5} "sweet spot" where fluctuations cause less energy shift and the anharmonicity is maximal. Transmon (large E J / E c {\displaystyle E_{J}/E_{c}} , bottom) energy levels are insensitive to fluctuations but the anharmonicity is reduced.
Transmon: A device consisting of four transmon qubits, four quantum buses, and four readout resonators fabricated by IBM and published in npj Quantum Information in January 2017.[4]
A device consisting of four transmon qubits, four quantum buses, and four readout resonators fabricated by IBM and published in npj Quantum Information in January 2017.[4]

Worked examples

Example 1 — a first encounter with Transmon

Start with the simplest possible case. Write down what Transmon 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 Transmon 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 Transmon 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 Transmon

In research
Transmon 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 Transmon 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
Transmon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Quantum electronics, Quantum information science, Superconductivity, so understanding it makes those chapters shorter.
In everyday life
Look for Transmon 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 Transmon in 20 minutes

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

Frequently asked questions

What is Transmon in simple terms?

In quantum computing, and more specifically in superconducting quantum computing, a transmon is a type of superconducting charge qubit designed to have reduced sensitivity to charge noise. The transmon was developed by Jens Koch, Terri M.

Why does Transmon 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 Transmon?

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 Transmon.

Tags

  • Quantum electronics
  • Quantum information science
  • Superconductivity

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