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Image Credit: Joint Quantum Institute - University of Maryland
What is decoherence?
Quantum decoherence is the loss of quantum coherence. In quantum mechanics, particles such as electrons are described by a wave function, a mathematical representation of the quantum state of a system; a probabilistic interpretation of the wave function is used to explain various quantum effects. Decoherence happens when different portions of the system's wave function become entangled in different ways with the measuring device.
# 3 criteria defined as : Long relevant decoherence times, much longer than the gate operation. As the decoherence time dictates the length of time the qubits can be entangled without loss of any information, any computation must be finished before the qubits loose information.
Here is a way to increase the coherence allowing for long-lasting coherence as prescribed by Kielpinski, David (Ph.D., Physics) on this paper published 2001. I include the link as a learning sample. His work has been used in many scientific papers:
"We observed a number of decoherence mechanisms in our register, the most prominent being magnetic field fluctuations and heating of the ion motion. We propose a way to eliminate the effects of heating. Finally, we implemented a decoherence-free quantum memory that was shielded from the effects of magnetic field fluctuations. Encoding one qubit’s worth of information in the decoherence-free subspace of two ions increased the memory lifetime by a factor of three under ambient conditions."
Important information:
Typical gate operation times for trapped ions range between 1µs and 1ms (A microsiemens (μS, uS) is a decimal fraction of the SI unit of electrical conductance and admittance siemens and is equal to 10⁻⁶ siemens. ), implying that decoherence time to gate time ratios of up to 10 to the power of 7 are currently achievable.
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