Comment by westurner | Hacker News Reader

Comment by westurner | Hacker News Reader

Parent Full thread

To just quote from Wikipedia:

"Qubit > Quantum register > Qudits and qutrits" https://en.wikipedia.org/wiki/Qubit#Qudits_and_qubits

> ## Qudits and qutrits

> The term qudit denotes the unit of quantum information that can be realized in suitable d-level quantum systems.[8] A qubit register that can be measured to N states is identical[c] to an N-level qudit. A rarely used[9] synonym for qudit is quNit, [10] since both `d` and N are frequently used to denote the dimension of a quantum system.

> Qudits are similar to the integer types in classical computing, and may be mapped to (or realized by) arrays of qubits. Qudits where the d-level system is not an exponent of 2 can not be mapped to arrays of qubits. It is for example possible to have 5-level qudits.

> In 2017, scientists at the National Institute of Scientific Research constructed a pair of qudits with 10 different states each, giving more computational power than 6 qubits.[11]

> Similar to the qubit, the qutrit is the unit of quantum information that can be realized in suitable 3-level quantum systems. This is analogous to the unit of classical information trit of ternary computers.

> ## Physical implementations [of qubits,]

> Any two-level quantum-mechanical system can be used as a qubit. Multilevel systems can be used as well, if they possess two states that can be effectively decoupled from the rest (e.g., ground state and first excited state of a nonlinear oscillator). There are various proposals. Several physical implementations that approximate two-level systems to various degrees were successfully realized. Similarly to a classical bit where the state of a transistor in a processor, the magnetization of a surface in a hard disk and the presence of current in a cable can all be used to represent bits in the same computer, an eventual quantum computer is likely to use various combinations of qubits in its design.

> The following is an incomplete list of physical implementations of qubits, and the choices of basis are by convention only: [...]

See also: "Quantum logic gate" https://en.wikipedia.org/wiki/Quantum_logic_gate

>> Quantum Monte Carlo: https://en.wikipedia.org/wiki/Quantum_Monte_Carlo :

>> Quantum Monte Carlo encompasses a large family of computational methods whose common aim is the study of complex quantum systems. One of the major goals of these approaches is to provide a reliable solution (or an accurate approximation) of the quantum many-body problem. [...] The difficulty is however that solving the Schrödinger equation requires the knowledge of the many-body wave function in the many-body Hilbert space, which typically has an exponentially large size in the number of particles. Its solution for a reasonably large number of particles is therefore typically impossible,*

> What sorts of independent states can or should we map onto error-corrected qubits in an approximating system?

> Propagation of Uncertainty ... Numerical stability ... Chaotic convergence, ultimately, apparently: https://en.wikipedia.org/wiki/Propagation_of_uncertainty

> Programming the Universe: https://en.wikipedia.org/wiki/Programming_the_Universe :

> Lloyd also postulates that the Universe can be fully simulated using a quantum computer; however, in the absence of a theory of quantum gravity, such a simulation is not yet possible. "Particles not only collide, they compute."

> Quantum on Silicon looks cheaper in today dollars.

Morello's,

> Devide [sic] the universe in QFT field-equal halves A and B, take energy from A to make B look like A, then add qubit error correction, and tell me if there's enough energy to simulate the actual universe on a universe QC with no instruction pipeline.

Due to error correction; propagation of uncertainty.

"Quantum computing in silicon hits 99% accuracy" (2022) https://www.eurekalert.org/news-releases/940321 :

> Quantum computing in silicon hits the 99% threshold

> Morello et al achieved 1-qubit operation fidelities up to 99.95 per cent, and 2-qubit fidelity of 99.37 per cent with a three-qubit system comprising an electron and two phosphorous atoms, introduced in silicon via ion implantation.

> A Delft team in the Netherlands led by Lieven Vandersypen achieved 99.87 per cent 1-qubit and 99.65 per cent 2-qubit fidelities using electron spins in quantum dots formed in a stack of silicon and silicon-germanium alloy (Si/SiGe).

> A RIKEN team in Japan led by Seigo Tarucha similarly achieved 99.84 per cent 1-qubit and 99.51 per cent 2-qubit fidelities in a two-electron system using Si/SiGe quantum dots.

>> The following is an incomplete list of physical implementations of qubits, and the choices of basis are by convention only: [...]

Qubit#Physical_implementations: https://en.wikipedia.org/wiki/Qubit#Physical_implementations

- note the "electrons" row of the table

> See also: "Quantum logic gate" https://en.wikipedia.org/wiki/Quantum_logic_gate

Reply on news.ycombinator.com