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arXiv:1006.2670 · Nature Communications

Adding control to arbitrary unknown quantum operations

Xiaoqi Zhou, Timothy C. Ralph, Pruet Kalasuwan, Mian Zhang, Alberto Peruzzo, B. P. Lanyon, Jeremy L. O’Brien

Published Aug 2, 2011• 173 citations
arXivHTMLPDF

Abstract

Although quantum computers promise significant advantages, the complexity of quantum algorithms remains a major technological obstacle. We have developed and demonstrated an architecture-independent technique that simplifies adding control qubits to arbitrary quantum operations—a requirement in many quantum algorithms, simulations and metrology. The technique, which is independent of how the operation is done, does not require knowledge of what the operation is, and largely separates the problems of how to implement a quantum operation in the laboratory and how to add a control. Here, we demonstrate an entanglement-based version in a photonic system, realizing a range of different two-qubit gates with high fidelity. Quantum computing has advantages over conventional computing, but the complexity of quantum algorithms creates technological challenges. Here, an architecture-independent technique, that simplifies adding control qubits to arbitrary quantum operations, is developed and demonstrated.

DOI
10.1038/ncomms1392

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Although quantum computers promise significant advantages, the complexity of quantum algorithms remains a major technological obstacle. We have developed and demonstrated an architecture-independent technique that simplifies adding control qubits to arbitrary quantum operations—a requirement in many quantum algorithms, simulations and metrology. The technique, which is independent of how the operation is done, does not require knowledge of what the operation is, and largely separates the problems of how to implement a quantum operation in the laboratory and how to add a control. Here, we demonstrate an entanglement-based version in a photonic system, realizing a range of different two-qubit gates with high fidelity. Quantum computing has advantages over conventional computing, but the complexity of quantum algorithms creates technological challenges. Here, an architecture-independent technique, that simplifies adding control qubits to arbitrary quantum operations, is developed and demonstrated.
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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.
Superconducting qubits are the promising candidate to realize large-scale quantum computing systems. Well-known quantum algorithms, such as Shor's algorithm, require at least10510^{5}105to10610^{6}106qubits to execute. Accordingly, classical systems for controlling superconducting qubits must also be scalable. One critical scalability challenge lies in the circuit cost of an RF pulse generator used to implement quantum gate operations. This poster proposes a cost-effective architecture for an RF pulse generator tailored to superconducting qubits. Most existing works use arbitrary waveform generators (AWGs) that require both a high-bandwidth memory (HBM) and a high-performance digital-analog converter (DAC) to achieve the highest gate fidelity with an optimized RF pulse waveform. The proposed pulse generator architecture significantly simplifies both the generator circuit and the waveform of the RF pulse to cost-aware square pulses. This architecture eliminates the requirement for power- and cost-intensive AWG, which is a major obstacle in realizing scalable quantum computers. Additionally, this poster demonstrates that our architecture can mitigate the error source associated with simplified RF pulses. Quantum dynamics simulation of transmon qubits, wherein the state of the system evolves with time, demonstrates that our pulse generator can achieve practically the same fidelity of gate operations for single and multiple qubits as ideal RF pulses while substantially reducing the sampling rate of DACs and the bandwidth of memories.
Abstract Quantum entanglement lies at the heart of quantum mechanics in both fundamental and practical aspects. The entanglement of quantum states has been studied widely both theoretically and experimentally, however, the entanglement of operators has not been studied much experimentally in spite of its importance. Here, we propose a scheme to realize arbitrary entangled operations based on a coherent superposition of local operations with a non-zero probability of failure. Then, we experimentally implement several intriguing two-qubit entangled operations in photonic systems. We also discuss the generalization of our scheme to extend the number of superposed operations and the number of qubits. Due to the simplicity of our scheme, we believe that it can reduce the complexity or required resources of the quantum circuits and provide insights to investigate properties of entangled operations.
This paper presents a novel high-order quantum entanglement computing framework designed to enhance computational efficiency and precision. The framework leverages advanced quantum entanglement to enable adaptive quantum algorithms, dynamically adjusting parameters to optimize performance. We explore the architectural design, core mechanisms, and potential benefits of this approach. The research focuses on overcoming limitations inherent in traditional quantum computing approaches, particularly concerning the ability to precisely control and manipulate entangled states. We demonstrate the framework's efficacy through theoretical analysis and preliminary experimental results, showcasing its potential to significantly improve the performance of complex quantum algorithms.
Minimizing the resources required to build logic gates into useful processing circuits is key to realizing quantum computers. Although the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analog has been realized. By adding control to the SWAP unitary, we use photonic qubit logic to demonstrate the first quantum Fredkin gate, which promises many applications in quantum information and measurement. We implement example algorithms and generate the highest-fidelity three-photon Greenberger-Horne-Zeilinger states to date. The technique we use allows one to add a control operation to a black-box unitary, something that is impossible in the standard circuit model. Our experiment represents the first use of this technique to control a two-qubit operation and paves the way for larger controlled circuits to be realized efficiently.