Quantum Computing Modalities
PostQuantum.com by Marin Ivezic – Quantum Computing Modalities and Architectures
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Quantum Computing Modalities: Superconducting Cat Qubits
Superconducting cat qubits are an emerging approach to quantum computing that still uses superconducting circuits but encodes each qubit in a bosonic mode - typically a microwave resonator - as a Schrödinger “cat” state (a superposition of two coherent states). In essence, instead of a single Josephson junction acting as a two-level qubit (like a transmon or flux qubit), a cat qubit stores quantum information in the joint state of…
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Taxonomy of Quantum Computing: Modalities & Architectures
Over the past few decades, researchers have devised multiple quantum computing paradigms – different models and physical implementations of quantum computers – each addressing these challenges in unique ways. In essence, there is no single “quantum computer” design; instead, there are many parallel approaches, each with its own principles, trade-offs, and technological hurdles.
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Quantum Computing Modalities: Photonic Cluster-State
Photonic Cluster-State Computing is a form of quantum computing in which information is processed using photons (particles of light) that have been prepared in a highly entangled state known as a cluster state. It falls under the paradigm of measurement-based quantum computing (MBQC), often called the one-way quantum computer. In this scheme, a large entangled resource state (the photonic cluster state) is generated first, and then the computation is carried…
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Quantum Computing Modalities: Ion Trap and Neutral Atom MBQC
Ion Trap and Neutral Atom implementations of MBQC leverage two leading “matter-qubit” platforms – trapped ions and ultracold neutral atoms – to realize this model. In a trapped-ion MBQC, a string of ions (charged atoms) is confined and entangled via electromagnetic fields and laser pulses. The ions’ internal states serve as qubits that can be entangled pairwise or globally using multi-ion gate operations, preparing a cluster state.
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Quantum Computing Modalities: Superconducting Qubits
Superconducting qubits are quantum bits formed by tiny superconducting electric circuits, typically based on the Josephson junction – a sandwich of two superconductors separated by a thin insulator which allows tunneling of Cooper pairs. When cooled to extremely low temperatures (≈10–20 millikelvin), these circuits exhibit quantized energy levels that can serve as the |0⟩ and |1⟩ states of a qubit.
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Quantum Computing Modalities: Holonomic (Geometric Phase) QC
Holonomic quantum computing (also known as geometric quantum computing) is a paradigm that uses geometric phase effects to perform quantum logic operations. In a holonomic gate, the quantum state is manipulated by adiabatically (or sometimes non-adiabatically) moving the system’s parameters along a closed loop in parameter space, causing the state to acquire a geometric phase or holonomy.
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Quantum Computing Modalities: Photonic QC
Photonic quantum computing uses particles of light – photons – as qubits. Typically, the qubit is encoded in some degree of freedom of a single photon, such as its polarization (horizontal = |0⟩, vertical = |1⟩), or its presence/absence in a given mode (occupation number basis: no photon = |0⟩, one photon = |1⟩ in a mode), or time-bin (photon arriving early vs late). Photons are appealing qubits because they…
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Quantum Computing Modalities: Trapped-Ion QC
Trapped-ion quantum computing uses individual ions (charged atoms) as qubits. Each ion’s internal quantum state (usually two hyperfine levels of the atom’s electron configuration) serves as |0⟩ and |1⟩. Ions are held in place (suspended in free space) using electromagnetic traps – typically a linear Paul trap that confines ions in a line using oscillating electric fields. By using lasers or microwaves to interact with the ions, quantum gates can…
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Quantum Computing Modalities: Adiabatic Topological QC (ATQC)
Adiabatic Topological Quantum Computing (ATQC) is a hybrid paradigm that combines adiabatic quantum computing with topological quantum computing. In essence, ATQC uses slow, continuous changes in a quantum system’s Hamiltonian (an adiabatic evolution) to perform computations, while encoding information in topologically protected states for inherent error resistance.
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Quantum Computing Modalities: Neuromorphic QC (NQC)
Neuromorphic quantum computing (NQC) is a cutting-edge paradigm that merges two revolutionary approaches to computing: neuromorphic computing and quantum computing. Neuromorphic computing is inspired by the architecture of the human brain – it uses networks of artificial neurons and synapses (often implemented in specialized hardware) to process information in a highly parallel and energy-efficient way, much like brains do.
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Quantum Computing Modalities: Topological Quantum Computing
Topological Quantum Computing is a paradigm that seeks to encode quantum information in exotic states of matter that have topological degrees of freedom, and to perform quantum gates by braiding or otherwise manipulating these topological objects. The central promise of topological QC is built-in error protection: information stored in a topological form is inherently protected from local noise by global properties (similar to how a knot’s existence doesn’t depend on…
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Quantum Computing Modalities: Adiabatic QC (AQC)
Adiabatic Quantum Computing (AQC) is a universal paradigm of quantum computing based on the adiabatic theorem of quantum mechanics. It generalizes the idea of quantum annealing beyond just optimization. In AQC, one encodes the solution of an arbitrary computation in the ground state of some problem Hamiltonian $H_{\text{problem}}$. Instead of applying discrete gates, one evolves the quantum state continuously under a time-dependent Hamiltonian $H(t)$ from an initial easy state to…
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Quantum Computing Modalities: Spin Qubits in Other Semiconductors & Defects
In addition to silicon, spin qubits can be realized in other solid-state systems. One well-known example is the nitrogen-vacancy (NV) center in diamond, which is a point defect where a nitrogen atom next to a vacancy in the carbon lattice creates an electronic spin-1 system that can be used as qubit.
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Quantum Computing Modalities: Silicon-Based Qubits
Silicon-based quantum computing refers to qubits implemented using silicon semiconductor technology, leveraging the existing CMOS fabrication infrastructure. The most common silicon qubit implementations are spin qubits – using the spin of an electron or the spin of an atomic nucleus embedded in silicon as a qubit.
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Quantum Computing Modalities: Measurement-Based Quantum Computing (MBQC)
Measurement-Based Quantum Computing (MBQC), also known as the one-way quantum computer, is a paradigm where quantum computation is driven entirely by measurements on an entangled resource state. Instead of applying a sequence of unitary gates to a register of qubits, MBQC starts with a highly entangled state of many qubits (typically a cluster state) and then performs single-qubit measurements in a carefully chosen order and basis.
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