![]() This puts a tough requirement on the phase noise of the control electronics. Qubit control signals need to have a better phase coherence than the qubits themselves over the full length of a coherent pulse sequence. Already a minimal amplitude drift or phase shift on one of the interfering paths is enough to move away from the optimal point significantly. In contrast, IQ mixing relies on an interferometric cancellation of signals for that purpose. What’s the explanation? Filtering, which is used in DSH to suppress unwanted sidebands, is hardly temperature dependent. That means there are now 3 spurious components in the 50 to 60 dBc amplitude range within several 100 MHz, not only one! In comparison, the DSH spectrum stays where it is: 72 dBc, independent of time and temperature. Upon a temperature change of a few degrees C, which can easily occur in a typical lab setting, the suppressed LO and image components rise in amplitude by 10 to 20 dB. Too many imperfections for the number of available knobs!Ī mixer calibration doesn’t stay fresh for too long. In the setup used in this paper, a second-order sideband limits the SFDR to 52 dBc even after a fresh calibration. But unfortunately, the imperfections don’t stop there: higher-order sidebands are next in line. By adjusting the relative amplitude and phase of the I and Q signals, one may suppress an undesired sideband at the mixer image frequency. By adding voltage offsets to the I and Q ports one may suppress an undesired signal at the local oscillator frequency - the LO leakage. One can tune knobs to iron out the imperfections of the analog world. How does that come about? A real IQ mixer is not as perfect a multiplier as its textbook mixer equation suggests. That’s 20 dB of safety margin which provides you with more freedom and peace of mind when choosing your transition frequencies. In the relevant operating conditions, Johannes Herrmann and coworkers measured a SFDR of 72 dBc in the DSH approach vs. In quantum computing, a spectrum free of spurious peaks means less risk of exciting unwanted transitions and less dephasing of the addressed qubit transition. Spurious-free dynamic range (SFDR) specifies the ratio in dB between a carrier signal amplitude and the largest unwanted peak within the specified bandwidth. DSH provides better spurious-free dynamic range over a wider frequency band Let’s look at these elements in more detail. It also removes the need for mixer calibration, a method that is both time-consuming and susceptible to temperature drift. Compared with IQ mixing, DSH gets you 20 dB better spurious-free dynamic range, and a comparable phase noise which is even superior in the low-frequency, or long-timescale limit. These results are complemented with characterization measurements of parameters important for achieving high-fidelity gate operations. The most exciting result: randomized benchmarking measurements hint at DSH enabling a higher gate fidelity and lower state leakage rate than a standard IQ mixing approach! Both methods allow for operation very close to the coherence limit of the used qubits, but further measurements are required to demonstrate a sizable improvement with higher coherence qubits. They compared the performance of our SHFSG Signal Generator with that of a high-quality IQ mixing setup similar to the HDIQ IQ Modulator. Were you ever curious about how double-superheterodyne (DSH) frequency conversion compares with IQ mixing when tested on real qubits? Johannes Herrmann and coworkers from the Quantum Device Lab at ETH Zurich have done exactly that and have recently made their findings available in a preprint paper. Non-Contact Atomic Force Microscopy (NC-AFM) Multi-Frequency Atomic Force Microscopy (MF-AFM) ![]() Tunable Diode Laser Absorption Spectroscopy Magnetometry with Ensembles of NV Centers Quantum Computing with Superconducting Qubits ![]()
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