Some quantum computing approaches use quantum dots

Some quantum computing approaches use quantum dots but not all. This paper discusses different approaches and designs.

https://arxiv.org/pdf/1804.10648.pdf

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VI. SUMMARY AND OUTLOOK

We have summarized the basic features and requirements
for quantum computing devices. This includes the fundamental
criteria that a quantum computing device must implement as
well as the the principles of operation for performing computation within the circuit model. We have reviewed the state of
the art in three specific technologies currently being developed
for quantum computing devices. Silicon spins, trapped ions,
and superconducting transmons represent three of the leading
approaches for quantum computing but these devices are
still face fundamental research challenges. Therefore, methods
to accurately characterize and benchmark the behavior of
quantum computing devices plays an important role in design
and testing. We have emphasized the necessity of statistical
analysis to infer the operation of quantum devices. We have
also discussed the design of optimal quantum circuits for the
case of arithmetic operations, which represent an important
use case for future quantum computing devices. These circuits were designed to minimize the occurrence of a specific
instruction, the T gate, due to the expected complexity of fault tolerant implementation. Such optimizations are expected to
play a critical role in future device operation as trade-offs in
gate and device complexity become more sophisticated.

The design and testing of early quantum computing devices
faces many near-term challenges. We have emphasized a small
subset of the technologies currently under investigation for
developing quantum computing devices. However, there are
many more approaches to be considered, each with their own
nuanced physics. This suggests that variations in the physics
of each quantum computing technology may lead to different
implementations for design and testing. Comparison across
technologies will require standard calibration techniques that
have yet to be developed. In addition, methods for quantifying
well-defined metrics will be important for evaluating device
performance. Current testing is focused on meeting the minimal criteria for functionality in the regime of noisy, error prone, and faulty devices. Finally, we note that the current
state of quantum computing remains focused on relatively
small scale devices. Future devices, or networks of devices, are
likely to include quantum registers with millions of elements
and sequences with millions of highly parallelized instructions.
Those devices and circuits will require more sophisticated
methods for design and testing.

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Of the three approaches discussed, the first, silicon spin, may or may not use QDs.

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A. Silicon Spin Qubits
Silicon spin qubits denote a technology implementation
by which quantum information is encoded either in the spin
states of an electron found in a silicon quantum dot , or in
the spin state of the electron or nucleus of a single-dopant
atom (typically group V donors) in a silicon substrate.

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The other two approaches do not use QDs.

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B. Trapped Ion Qubits

Trapped ion qubits represent an implementation where
quantum information is encoded in the electronic energy levels
of ions suspended in vacuum.

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C. Superconducting Transmon Qubits

The device geometry for transmon qubits consists of two
superconducting islands that are coupled through two Josephson junctions and a large capacitance between them (Fig.
4a).

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So there may or may not be a market for QDs in quantum computing beyond current research efforts.