Multiplexed readout
Often due to physical limitations we want to have the ability to use one transmission line or one cavity to interact with multiple qubits with different resonance frequencies. A common technique used in communication systems is to use FDM (Frequency division multiplexing) where numerous signals with different central frequency are combined on a single composite signal which carries all the information. It's made possible by the simple fact that pure signals with different frequencies are orthogonal. A requirement for the protocol is to divide the bandwidth for the desired signals such that there's no overlap in the frequency domain.
#
ConfigWe define three quantum elements rr1,rr2,rr3
corresponding to three readout resonators.
Each rr
is defined with its own resonance frequency, these should be distant enough to enable the FDM protocol.
We also define a readout
operation for all the resonators. Notice that the input/output ports for all rr
elements
are the same, and this is because we 'communicate' with them through the same transmission line.
For simulation purposes the readout pulses for each element is different, and simulate g,e,f states using the Loopback Interface.
#
ProgramFirstly, currently it's only possible to do up to 10 parallel demodulations per device, therefore we readout up to 2 resonators at the same time, because each requires 4 real demodulations. The code is written generally to allow a readout of an arbitrary number of resonators.
To begin the program we align
all the resonators, which ensure a simultaneous measurement of all elements.
Next, we use the measure
command in a for loop to measure all the rr's.
Then, we wait
on all elements and let the resonator/transmission line relax.
Finally, we save the IQ components for each resonator to its corresponding variable,
i.e measurement from rr2
is saved to variable I2
and Q2
.
#
Post ProcessingFor illustration purposes, we fetch the results of each resonator and plot the IQ diagram.
Since in our example we use a ground state pulse for the rr1
and excited state pulse for rr2
we expect to get one 'blob' for each resonator.
We can verify the the frequency multiplexing worked since the blobs are well separated as excpected for different qubit state.