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Qubit

About: Qubit is a research topic. Over the lifetime, 29978 publications have been published within this topic receiving 723084 citations. The topic is also known as: quantum bit & qbit.


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Journal ArticleDOI
TL;DR: In this paper, a model of quantum computation with local fermionic modes (LFMs), sites which can be either empty or occupied by a fermion, was defined and the simulation cost was reduced to O(log m) and a constant.

756 citations

01 May 2003
TL;DR: In this article, the authors demonstrate a universal geometric pi-phase gate between two beryllium ion-qubits, based on coherent displacements induced by an optical dipole force.
Abstract: Universal logic gates for two quantum bits (qubits) form an essential ingredient of quantum computation. Dynamical gates have been proposed in the context of trapped ions; however, geometric phase gates (which change only the phase of the physical qubits) offer potential practical advantages because they have higher intrinsic resistance to certain small errors and might enable faster gate implementation. Here we demonstrate a universal geometric pi-phase gate between two beryllium ion-qubits, based on coherent displacements induced by an optical dipole force. The displacements depend on the internal atomic states; the motional state of the ions is unimportant provided that they remain in the regime in which the force can be considered constant over the extent of each ion's wave packet. By combining the gate with single-qubit rotations, we have prepared ions in an entangled Bell state with 97% fidelity-about six times better than in a previous experiment demonstrating a universal gate between two ion-qubits. The particular properties of the gate make it attractive for a multiplexed trap architecture that would enable scaling to large numbers of ion-qubits.

746 citations

Journal ArticleDOI
12 Apr 2012-Nature
TL;DR: In this article, the authors present a prototype of a quantum network based on single atoms embedded in optical cavities and demonstrate the faithful transfer of an atomic quantum state and the creation of entanglement between two identical nodes in separate laboratories.
Abstract: Quantum networks are distributed quantum many-body systems with tailored topology and controlled information exchange. They are the backbone of distributed quantum computing architectures and quantum communication. Here we present a prototype of such a quantum network based on single atoms embedded in optical cavities. We show that atom–cavity systems form universal nodes capable of sending, receiving, storing and releasing photonic quantum information. Quantum connectivity between nodes is achieved in the conceptually most fundamental way—by the coherent exchange of a single photon. We demonstrate the faithful transfer of an atomic quantum state and the creation of entanglement between two identical nodes in separate laboratories. The non-local state that is created is manipulated by local quantum bit (qubit) rotation. This efficient cavity-based approach to quantum networking is particularly promising because it offers a clear perspective for scalability, thus paving the way towards large-scale quantum networks and their applications. Single atoms in optical cavities in two separate laboratories are the nodes of an elementary quantum network, in which quantum information is distributed via the controlled emission and absorption of single photons. Quantum networks, following the principles of quantum teleportation, form the backbone of distributed quantum-computing architectures and quantum communication. This paper reports the first realization of an elementary quantum network with two quantum nodes based on single atoms trapped in optical cavities in separate laboratories. The approach is particularly promising in that it demonstrates all the necessary ingredients of a full-scale quantum network.

742 citations

Journal ArticleDOI
TL;DR: An architecture that exponentially reduces the requirements for a memory call: O(logN) switches need be thrown instead of the N used in conventional RAM designs, which yields a more robust QRAM algorithm, as it in general requires entanglement among exponentially less gates, and leads to an exponential decrease in the power needed for addressing.
Abstract: A random access memory (RAM) uses $n$ bits to randomly address $N={2}^{n}$ distinct memory cells. A quantum random access memory (QRAM) uses $n$ qubits to address any quantum superposition of $N$ memory cells. We present an architecture that exponentially reduces the requirements for a memory call: $O(\mathrm{log} N)$ switches need be thrown instead of the $N$ used in conventional (classical or quantum) RAM designs. This yields a more robust QRAM algorithm, as it in general requires entanglement among exponentially less gates, and leads to an exponential decrease in the power needed for addressing. A quantum optical implementation is presented.

741 citations

Journal ArticleDOI
TL;DR: In this paper, the full power of modern electronic band-structure engineering and epitaxial heterostructures was applied to design a transistor that can sense and control a single-donor electron spin.
Abstract: We apply the full power of modern electronic band-structure engineering and epitaxial heterostructures to design a transistor that can sense and control a single-donor electron spin. Spin-resonance transistors may form the technological basis for quantum information processing. One- and two-qubit operations are performed by applying a gate bias. The bias electric field pulls the electron wave function away from the dopant ion into layers of different alloy composition. Owing to the variation of the g factor (Si: g1.998,Ge:g1.563), this displacement changes the spin Zeeman energy, allowing single-qubit operations. By displacing the electron even further, the overlap with neighboring qubits is affected, which allows two-qubit operations. Certain silicon-germanium alloys allow a qubit spacing as large as 200 nm, which is well within the capabilities of current lithographic techniques. We discuss manufacturing limitations and issues regarding scaling up to a large size computer.

722 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,977
20224,380
20213,014
20203,119
20192,594
20182,228