Quantum computing tries to exploit entanglement and interference to process information more efficiently than the best known classical solutions. Experiments demonstrating the feasibility of this approach have already been performed. However, finding a really scalable and robust quantum computing architecture remains a challenge for both, experimentalists and theoreticians. In most setups decoherence becomes non-negligible when one tries to perform entangling gate operations using the coherent control of qubit-qubit interactions. However, in this proceedings we show that two-qubit gate operations can be implemented even without qubit-qubit interactions and review a recent quantum computing scheme by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)] using only single photon sources (e.g. atom-cavity systems, NV colour centres or quantum dots) and photon pair measurements.
Quantum computing tries to exploit entanglement and interference to process information more efficiently than the best known classical solutions. Experiments demonstrating the feasibility of this approach have already been performed. However, finding a really scalable and robust quantum computing architecture remains a challenge for both, experimentalists and theoreticians. In most setups decoherence becomes non-negligible when one tries to perform entangling gate operations using the coherent control of qubit-qubit interactions. However, in this proceedings we show that two-qubit gate operations can be implemented even without qubit-qubit interactions and review a recent quantum computing scheme by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)] using only single photon sources (e.g. atom-cavity systems, NV colour centres or quantum dots) and photon pair measurements.
Quantum computing is emerging as a revolutionary paradigm in the field of computing, promising an exponential leap in computing power and problemsolving that challenges even the most advanced supercomputers of the classical era.At the heart of this revolution lies the peculiarity of the quantum world, where subatomic particles can exist in multiple states simultaneously, a phenomenon known as superposition, and entangle their states in a way that defies classical logic.It is this capacity for superposition and entanglement that gives quantum computing its disruptive power.One of the most intriguing properties of quantum computing is its ability to process information using Qubits, the quantum analogues of classical bits.While a classical bit can only be in a single 0 or 1 state, a Qubit can simultaneously represent a 0, a 1, or any superposition of these states, allowing multiple calculations to be performed in parallel.This massively parallel processing capability is the basis for the potential superiority of quantum computers over their classical counterparts in a wide range of applications.The architecture of quantum computers is inherently different from classical computers.While the latter use transistors to store and manipulate information in bits, quantum computers use Qubits, which can be implemented in a variety of physical systems, such as atoms, ion traps, photons, superconductors or nuclear magnetic resonance.The manipulation of the Qubits is carried out through quantum gates, fundamental operations that transform the quantum state of the Qubits and allow quantum calculations to be carried out.Furthermore, to maintain quantum coherence, the control and isolation of the quantum system from its environment is crucial, posing significant challenges in terms of designing and building scalable and robust quantum systems.
In this paper, we look at the possibility of realizing one-way quantum computing through a hybrid quantum computing architecture based on stationary qubits inside an optical cavity and flying qubits (photons). It has been shown that direct qubit-qubit interactions for two-qubit gate implementations can be replaced by the experimentally less demanding generation of single photons on demand and linear optics photon pair measurements. The outcomes of these measurements indicate either the completion of the gate or the presence of the original qubits, such that the operation can be repeated until success.
We introduce an architecture for robust and scalable quantum computation using both stationary qubits (e.g., single photon sources made out of trapped atoms, molecules, ions, quantum dots, or defect centers in solids) and flying qubits (e.g., photons). Our scheme solves some of the most pressing problems in existing nonhybrid proposals, which include the difficulty of scaling conventional stationary qubit approaches, and the lack of practical means for storing single photons in linear optics setups. We combine elements of two previous proposals for distributed quantum computing, namely the efficient photon-loss tolerant build up of cluster states by Barrett and Kok [Phys. Rev. A 71, 060310(R) (2005)] with the idea of repeat-until-success (RUS) quantum computing by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)]. This idea can be used to perform eventually deterministic two qubit logic gates on spatially separated stationary qubits via photon pair measurements. Under nonideal conditions, where photon loss is a possibility, the resulting gates can still be used to build graph states for one-way quantum computing. In this paper, we describe the RUS method, present possible experimental realizations, and analyze the generation of graph states.
We show that it is possible to employ reservoir engineering to turn two distant and relatively bad cavities into one good cavity with a tunable spontaneous decay rate. As a result, quantum computing schemes, which would otherwise require the shuttling of atomic qubits in and out of an optical resonator, can now be applied to distant quantum dots. To illustrate this we transform a recent proposal to entangle two qubits via the observation of macroscopic fluorescence signals [J. Metz et al., Phys. Rev. Lett. 97, 040503 (2006)] to the electron-spin states of two semiconductor quantum dots. Our scheme requires neither the coherent control of qubit-qubit interactions nor the detection of single photons. Moreover, the scheme is relatively robust against spin-bath couplings, parameter fluctuations, and the spontaneous emission of photons.
This article provides a comprehensive technical examination of quantum computing systems based on qubit technology, exploring their revolutionary potential to transform computational capabilities beyond classical limitations. Beginning with an analysis of the fundamental quantum mechanical principles—superposition, entanglement, and quantum interference—the article elucidates how these phenomena enable exponential computational advantages for specific problem domains. Various physical implementations of qubits are evaluated, including superconducting circuits, trapped ions, photonic systems, and theoretical topological approaches, with each platform presenting unique advantages and engineering challenges. It extends to practical applications across cryptography, optimization, and artificial intelligence, where quantum computing promises transformative capabilities. However, significant obstacles remain, including decoherence, high error rates, scalability limitations, and the ongoing development of practical quantum algorithms. Despite these challenges, the quantum computing landscape is evolving toward a hybrid paradigm where quantum and classical resources work in concert, with specialized quantum processors likely to deliver commercial value in specific domains before universal quantum computers become a reality.