Short version:
Quantum computing and modern microwave engineering share a common ancestor in the pioneering work that led to the development of radar and related technologies in the 1940’s . Indeed, many of the fundamental mechanisms underpinning the generation, transmission, absorption, and detection of microwave energy were understood at that time to be governed by quantum mechanics, which describes the light-matter interaction between microwaves and atoms or molecules , as well as their constituent charge and spin states . The leveraging of war-time radar technology and methods in the discovery of nuclear magnetic resonance in solids provides an ideal example of the long-standing synergy between microwave engineering and quantum systems .
At the bottom of the link see the Plank constant information.
Much longer version with the original document link provided and a free downloadable copy in PDF:
Quantum information processing systems rely on a broad range of microwave technologies and have spurred development of microwave devices and methods in new operating regimes. Here we review the use of microwave signals and systems in quantum computing, with specific reference to three leading quantum computing platforms: trapped atomic ion qubits, spin qubits in semiconductors, and superconducting qubits. We highlight some key results and progress in quantum computing achieved through the use of microwave systems, and discuss how quantum computing applications have pushed the frontiers of microwave technology in some areas. We also describe open microwave engineering challenges for the construction of large-scale, fault-tolerant quantum computers.
Keywords: Semiconductor spin qubit, superconducting qubit, trapped ion qubit, quantum computing, qubit control, qubit readout, quantum-classical interface.
Quantum computing and modern microwave engineering share a common ancestor in the pioneering work that led to the development of radar and related technologies in the 1940’s . Indeed, many of the fundamental mechanisms underpinning the generation, transmission, absorption, and detection of microwave energy were understood at that time to be governed by quantum mechanics, which describes the light-matter interaction between microwaves and atoms or molecules , as well as their constituent charge and spin states . The leveraging of war-time radar technology and methods in the discovery of nuclear magnetic resonance in solids, provides an ideal example of the long-standing synergy between microwave engineering and quantum systems.
Fundamental to this light-matter interaction is the relation E = ℏω, which connects the angular frequency ω of microwave photons to their energy E (ℏ is the reduced Planck’s constant - = 6.62607015×10−34 J⋅Hz−1). The quantization( to subdivide (something, such as energy) into small but measurable increments. 2 : to calculate or express in terms of quantum mechanics) of microwave energy describes how microwave photons can interact resonantly with other quantum objects, such as the quantum two-level systems (called qubits) that form the building blocks of quantum computers. Today, microwave technology is ubiquitous across many different quantum platforms, enabling the precise control and readout of quantum states. Here, we review the use of microwaves in quantum computing. For the sake of brevity, rather than surveying the complete quantum computing landscape, we focus on three leading qubit technologies: trapped ion qubits, semiconductor spin qubits, and superconducting circuit qubits.
We chose these technologies not only because they span the representative qubit technologies and are currently considered among the most promising of all qubit types, but also because they are heavily reliant on microwave technologies (see Fig. 1). The paper is organized as follows:
Picture:
\Microwave electronics for operating a 50-qubit Google quantum processor. The system generates and receives signals in the 4–8 GHz band, and was used to execute a demonstration quantum computing algorithm designed to be too complex for simulation by even the largest classical supercomputers [7]. Four racks of microwave electronics are required to control and measure the quantum processor.
Abbreviations: BB–baseband, AWG–arbitrary waveform generator, SSB–single sideband. Photo credit: R. Ceselin./
An overview of qubits and quantum processors is presented; the analogy between a qubit and a microwave resonator is explained, with implications discussed; and physical qubit realizations are described.
The coupling of a microwave source to various qubit technologies is described and typical signal and noise levels are compared and contrasted.
The quantum gate abstraction is explained, microwave techniques for implementing single and two qubit quantum gates are described, and typical hardware configurations are presented.
Microwave techniques for measuring the state of a qubit are described.
Additional microwave techniques required for the operation of trapped-ion qubits are described.
Microwave innovations in quantum-limited amplifiers and non-reciprocal devices, driven by quantum computing research, are presented.
Outstanding challenges related to microwave engineering that must be overcome to realize the full potential of quantum computing are described.
Next post: Detailed description of qubits and quantum processors
Planck constant: = 6.62607015×10−34 J⋅Hz−1
The Planck constant, or Planck's constant, denoted h is a physical constant that is the quantum of electromagnetic action, which relates the energy carried by a photon to its frequency. A photon's energy is equal to its frequency multiplied by the Planck constant. The Planck constant is of fundamental importance in quantum mechanics, and in metrology it is the basis for the definition of the kilogram.
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