Traveling-Wave Parametric Amplifier with Passive Reverse Isolation

Josephson junction traveling-wave parametric amplifiers (JTWPAs) have become an invaluable tool, providing broadband amplification and low-noise readout. Operating as two-port amplifiers, JTWPAs are intrinsically non-reciprocal, delivering forward gain and typically minimal attenuation in the reverse direction, mainly due to transmission line losses. However, JTWPAs are prone to unwanted internal reflections, which can redirect amplified signals back to the input port and interfere with the device under test. Managing these reflections is challenging because they occur within the amplifier's operating bandwidth, necessitating bulky microwave isolators that are hard to scale. Experimental methods for achieving reverse isolation in JTWPAs have primarily used parametric processes involving counterpropagating pumps, which upconvert backward-propagating signals. These methods demand additional hardware, require careful tuning of JTWPA nonlinearities, and the introduction and tuning of dual counterpropagating pumps in a complex phase-matching processes.



We introduce a JTWPA design that leverages a four-wave mixing parametric process with a single pump to achieve broadband forward amplification alongside reverse isolation across the same frequency band. The amplifier operates near the quantum noise limit throughout its usable bandwidth. We validate its versatility in a practical measurement setup by demonstrating effective performance without microwave isolators.