Demonstration of controlled-NOT quantum gates on a pair of superconducting quantum bits

Quantum computation requires quantum logic gates that use the interaction within pairs of quantum bits (qubits) to perform conditional operations. Superconducting qubits may offer an attractive route towards scalable quantum computing. In previous experiments on coupled superconducting qubits, condi...

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Bibliographic Details
Published in:Nature 2007-06, Vol.447 (7146), p.836-839
Main Authors: Plantenberg, J. H, Mooij, J. E, de Groot, P. C, Harmans, C. J. P. M
Format: Article
Language:English
Subjects:
Algorithms
Applied sciences
Circuit properties
Computation
Detectors
Digital circuits
Electric, optical and optoelectronic circuits
Electronic circuits
Electronics
Exact sciences and technology
Gates
Humanities and Social Sciences
letter
Logic
multidisciplinary
Phase shift
Quantum theory
Qubits (quantum computing)
Science
Science (multidisciplinary)
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Superconducting devices
Superconductivity
Superconductors
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Summary:Quantum computation requires quantum logic gates that use the interaction within pairs of quantum bits (qubits) to perform conditional operations. Superconducting qubits may offer an attractive route towards scalable quantum computing. In previous experiments on coupled superconducting qubits, conditional gate behaviour and entanglement were demonstrated. Here we demonstrate selective execution of the complete set of four different controlled-NOT (CNOT) quantum logic gates, by applying microwave pulses of appropriate frequency to a single pair of coupled flux qubits. All two-qubit computational basis states and their superpositions are used as input, while two independent single-shot SQUID detectors measure the output state, including qubit-qubit correlations. We determined the gate's truth table by directly measuring the state transfer amplitudes and by acquiring the relevant quantum phase shift using a Ramsey-like interference experiment. The four conditional gates result from the symmetry of the qubits in the pair: either qubit can assume the role of control or target, and the gate action can be conditioned on either the 0-state or the 1-state. These gates are now sufficiently characterized to be used in quantum algorithms, and together form an efficient set of versatile building blocks.
ISSN:0028-0836
1476-4687
1476-4679
DOI:10.1038/nature05896