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Quantum Computer

01 /Quantum Computers 02 /How to build a qubit 03 /Spin qubits (beginner level) 04 /Operations on spin qubits (beginner level) 05 /Electron spin qubits 06 /Capturing a single electron 07 /Quantum dot qubits 08 /Quantum control and readout 09 /Qubit errors 10 /NV center qubits 11 /Operations on NV center qubits 12 /The Transmon Qubit - A basis for the Quantum Computer 13 /Operations on the Transmon Qubit - Circuit QED 14 /Single-qubit operations on the Transmon qubit 15 /Measurements on the Transmon Qubit 16 /Two-qubit operations on the Transmon qubit 17 /Topological qubits: Anyons 18 /Operations on anyons: Braiding 19 /Operations on anyons: Real-life experiments 20 /Topological quantum computing: Majorana fermions and where to find them 21 /Majorana bound states in superconductors 22 /How do you measure Majorana bound states? 23 /A framework for the future Quantum Computer 24 /The Building Blocks of a Quantum Computer 25 /How to build a Quantum Algorithm - Quantum Circuits 26 /How do you program a quantum algorithm? 27 /The compiler of a quantum computer 28 /Micro-architectures 29 /How do we connect our quantum system to a classical interface? 30 /Assembling a Quantum Processor 31 /Microwave drivers for qubits 32 /Implementation of microwave drivers 33 /Quantum error correction 34 /Surface codes 35 /Fault-tolerant Quantum Error Correction with surface codes

Spin qubits (beginner level)

Time for another type of qubits: spin qubits. Heavily based on the concept of transistors (the building block of classical computers), these qubits are very suitable for use in quantum circuits. 

For these qubits, we need to trap single (!) electrons so that we can use its spin as the qubit. Wait... single electrons? Yes, and not only do we need to trap them, but we also need to know that we succeeded. How can we do this?

In this video, QuTech professor Lieven Vandersypen takes you through the basics of spin qubits. He first introduces the concepts of charging energy and Coulomb blockade, after which he explains how we can use it to form our qubit. Then Lieven explains charge sensing, yet another way to detect whether you have a single electron in your quantum dot. Finally, we take a look at scaling up our system, initially by looking at a system that consists of two quantum dots. Professor Vandersypen ends the video with a brief outlook on how spin qubits can ultimately be used in large-scale quantum integrated circuits.

 

Prerequisite knowledge

  • Quantum bits
  • Electrochemical potentials (i.e., energy diagrams)
  • (nice to have) Standard knowledge on transistors

Further thinking

We have seen that to realize spin qubits it is important to understand how quantum dots work. Do you understand why using a quantum dot is crucial?

Solution

Further reading 

Take a look at this review paper discussing the field of spins in quantum dots.

For more recent research, you might want to check out these papers:

In the paper by Watson et al. (2018), they show the experimental realisation of two quantum algorithms with a two spin qubits quantum processor.