![]() ![]() In this scenario we have a fantastically ideal laser that always raises the electromagnetic field to the same pure quantum state. Let's try to understand the underlying physics more deeply. Notwithstanding apparent "incoherence" effects cause the "fading" or lack of fringe visibility in the high power picture, you'll still see "lack of fringe visibility" show up extremely precisely in your probability densities even though we are dealing with pure quantum light states. The probability to detect at a given point is exactly proportional to the intensity of the high power field you saw before turning the light level down. ![]() Now turn your laser down so that there is "one photon in the kit at one time" and take zillions of measurements of single detection events at all places in space. Turn the laser up and remove all attenuators so that you can see interference fringes, where they fade out and other "coherence / incoherence" effects. If this mechanism is what is causing your inability to see fringes, then the answer to your question is very simple. Energy Spectral Spread with Pure Quantum States ![]() These events are individual detections of an idealized photomultiplier tube, which tells you it has interacted with the EM field, and at the same time the EM field drops back to its ground state.ġ. ![]() We're talking about the electromagnetic field in a "one photon state" - this simply means the electromagnetic field has been raised one "notch" above its ground state and is undergoing unitary evolution such that statistics of the potential measurement events vary with time. Our results are relevant for ongoing efforts towardīuilding superconducting quantum annealers with increased coherence.There isn't a straight answer to this question, which sheds light onto the meaning of the subtle word coherence, because what we tend to call "decoherence" can have two main roots.Ī practical experimental meaning of the word coherence is "ability to show interference", and there are two ways whereby observable interference can disappear: ( 1) (energy) spectral spread within the pure quantum states in question ( 2) genuine quantum decoherence.īefore we address these mechanisms, we need to be very clear on dispelling the notion of a "photon" as a little ball with schizophrenia and I'd urge you to read Daniel Sank's Most Wonderful Description Here and my commentary on his answer here: the only actors in the scene we'll discuss are ( 1) THE electromagnetic field and ( 2) the measuring instruments in your laboratory. Qubit loops, possibly due to non-local sources of flux noise or junctionĬritical-current noise. Of the dephasing time also reveals apparent noise correlation between the two Noise of control electronics used for fast annealing. In the two qubit loops, with additional contribution from the low-frequency Measured dephasing rate is primarily due to intrinsic low-frequency flux noise At higher frequencies, thermal noise in the bias line makesĪ significant contribution to the relaxation, arising from the design choice toĮxperimentally explore both fast annealing and high-frequency control. To intrinsic flux noise in the main qubit loop for qubit frequencies below The measured relaxation at the qubit symmetry point is mainly due Trappen and 21 other authors Download PDF Abstract: We present a detailed study of the coherence of a tunableĬapacitively-shunted flux qubit, designed for coherent quantum annealingĪpplications. Download a PDF of the paper titled Decoherence of a tunable capacitively shunted flux qubit, by R. ![]()
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