4
$\begingroup$

Often you see input/output ports for superconducting qubits looking like this block, which tapers down to a narrow transmission line: enter image description here

what is the reason for this tapering, and how do you actually read the microwave signals from these ports?

$\endgroup$
5
  • $\begingroup$ Can you provide a link to an image showing this? $\endgroup$ Jul 31 '18 at 15:56
  • $\begingroup$ I'm looking at @DanielSank's PhD thesis. $\endgroup$
    – wcc
    Jul 31 '18 at 16:45
  • $\begingroup$ Which is a 247-page document. Can you provide a page number? $\endgroup$ Jul 31 '18 at 16:47
  • $\begingroup$ @BillyKalfus, my bad, please take a look at page 109. $\endgroup$
    – wcc
    Jul 31 '18 at 16:56
  • $\begingroup$ Hi there. The taper is to keep the impedance of the transmission line roughly constant while we expand the line to be wide enough for a wire bond connection. $\endgroup$
    – DanielSank
    Sep 8 '18 at 5:59
2
$\begingroup$

This feature is used so that wires can be bonded to the transmission line. The end of the transmission line itself does not have enough area to reliably bond a wire to, so it opens up to a region of larger area (page 116 of Daniel Sank's thesis explicitly refers to this feature as a "bond pad").

The bonded wire is then brought to a connector, which passes the signal through a readout chain consisting of demodulators and filters. The actual architecture of the readout chain can differ depending on who designed it (see page 127 for one example), but will typically consist of demodulators, amplifiers, and filters that prepare the signal for measurement with an analog-to-digital converter.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.