(a) Experimental characterization of the circuit switching speed using different types of control signal. Here, a 100 MHz sinusoidal signal is transmitted through a single unit cell sample of the TLM, and the envelope of the output waveform is recorded (black curve). We activate the switch inside the unit cell using different types of control signals V sw , with drastically different slopes. Both a rectangular control signal (top) and a triangular control signal (bottom) produced identical output envelopes, demonstrating that the rise time of V sw has very little influence on the switching speed of the circuit. (b) A sample measurement of the control signal used to induce the time-interface. The slew rate of the signal is very low, due to the input reactance of the switches. However as shown in panel (a), simply crossing the activation threshold of the switch (2.3 V according to the datasheet) is sufficient to induce a sharp time-interface. This particular control signal was used to induce the time-interface examined in Fig. 2e of the main text. To further verify the fidelity of the time interface, we perform circuit simulation of the TLM with different 10%-to-90% rise time for the switches, and plot the (c) time domain voltage measured at the input port. The input is a Gaussian wave packet with 50 MHz center frequency and 40 MHz spectral FWHM. The blue curve represents the simulation results when the circuit has the same rise time (3 ns) as our selected RF switches; it is seen to closely match the black curve, which corresponds to the case when the rise time is near zero. As we further increase the rise time to 8 ns (green) and 12 ns (yellow), the amplitude of the time reflection become significantly weaker. (d) Peak amplitude (normalized against the ideal case) of the time reflected wave packet as a function of the switch rise time. The amplitude corresponding to the case of 3 ns rise time was approximately 90% of the ideal amplitude.