Types of Quantum Computers

5 min readAug 12, 2023

Day 12 — Quantum30 challenge

In today’s video for

’s challenge, an overview of the whole Quantum Computing field was shared which was an outline of the basics, algorithms, different types of quantum computers, challenges, and potentials. This was a very diverse video and I was confused about what to include in my article. If I had time, I would’ve included everything, but for now, for now, let’s just discuss the different models of quantum computers discussed in the video.

Terms to be known

Superposition

Entanglement

Quantum Computer

In the realm of computing, classical computers come in various architectures, such as digital, analog, Harvard, and von Neumann. Similarly, quantum computers exhibit diverse architectures that depend on the nature of qubits and how they can be controlled and manipulated. Let’s delve into some of these architectures and their qubit manipulation techniques.

Gate-based Quantum Computer

These are inspired by the traditional logic gates (AND, OR, NAND, etc.) used in normal computers. In Quantum Computers, we have special gates for computing like Pauli gates, Hadamard gates, Rotation gates, etc. which are applied to the qubits. The computation is represented as quantum circuits and finally, we measure it after the gates are applied.

Superconducting Quantum Computing

A Superconductor is a special type of material that has zero electrical resistance. The qubits are implemented using superconducting loops and circuits. Here, the two states are not |0> and |1> but the ground and excited states respectively, and are denoted by |g> and |e> respectively.

There are many different types of superconductors

Transmon Qubits: Transmons are a widely used type of superconducting qubits. They are based on a nonlinear oscillator design and can have longer coherence times (the time during which quantum information is preserved) compared to some other qubit types.
Xmon Qubits: Xmons are a variation of transmon qubits designed with a different geometry that improves qubit-qubit connectivity, making them suitable for building larger quantum processors.
Flux Qubits: Flux qubits use the superconducting properties of Josephson junctions to encode quantum information. They can have strong interactions with other qubits, which is useful for certain quantum operations.

Trapped ion quantum computers

Here, ions are trapped in electromagnetic fields. The qubits are usually encoded in the internal state of individual atoms. From these ions, there are 2 types of qubits which we can form

Hyperfine qubits: The energy level of both ions is degenerate which in simple terms means they are the same
Optical qubits: Formed by one ground state and one excited state of two ions respectively.

Lasers are used for manipulation of the qubits like performing entanglement, gate operations, etc.

Neutral atom Quantum computing

Parallel to trapped ions, here, we have neutral atoms which are trapped inside the electromagnetic field. There are different trapping techniques such as the optical trap, magnetic trap, magneto-optical trap, etc. The qubits are encoded in the internal state of the individual atoms. Lasers are used for the manipulation of the qubits and also for gate operations.

Quantum Dots Quantum computers

Quantum Dots are tiny semiconductor nanocrystals that can trap individual electrons or other charge carriers. The qubit state depends on the individual electrons trapped inside the dot and the state is represented by its spin. The manipulation of these qubits is done by microwave pulses or by applying electric or magnetic fields externally.

Optical Quantum Computers

Here we use photons as qubits and thus are also known as photonic qubits. The quantum state can be polarization, frequency, or phases of the qubits. the superposition and entanglement are created using wave plates whereas the qubit manipulation is done by optical instruments like beam splitter, phase shifters, etc. For gate implementation, normal quantum gates are used.

Color center quantum computers

(This was my first time learning about them). Color centers are defects in the solid state. Defects result from missing or substituted atoms in the crystal lattice. The qubits are embedded into these defects. The quantum states of color centers are often encoded in their electronic and nuclear spin states. The ground and excited states of color centers can be used to represent qubit states. The qubits are manipulated using laser lights to create superposition and entanglement.

NMR Quantum Computers

These use the principles of NMR(Nuclear Magnetic Resonance) for quantum computation. NMR is a phenomenon that occurs when the nuclei of certain atoms, such as hydrogen, respond to a magnetic field by emitting or absorbing radiofrequency electromagnetic radiation. Here, qubits are typically encoded in the nuclear spins of certain atoms in a molecule. The manipulation is done using radiofrequency pulses.

Electron on Helium Qubit Computing

Electrons are trapped on the surface of Superfluid helium and serve as qubits. Superfluid helium is a state of helium that exhibits unique properties due to its extremely low temperature. It lacks viscosity and can flow without friction. On the surface of superfluid helium, a two-dimensional layer forms, creating a quantum well where electrons can be trapped. This confines the electron and keeps the electron localized in a small region and allows for precise control over its quantum properties. Manipulations are done by external magnetic and electric fields.

Conclusion

This diversity of approaches reflects the intricate nature of quantum mechanics. While we’re still in the early stages of realizing the full potential of quantum computing, the progress made in each of these architectures marks significant strides toward solving complex problems that were previously beyond the capabilities of classical computers. The journey ahead involves continued research, innovation, and collaboration across disciplines, as we seek to unlock the true power of quantum computation and revolutionize industries ranging from cryptography to drug discovery.