Doctoral Thesis: The Quest for Ideal Quantum Amplifiers

Kaidong Peng

Abstract:

Faithful amplification and detection of weak signals are vital to a wide range of research fields, from quantum computing and dark matter detection to metrology and space communications. The increasingly complex systems for computing, metrology, and communication require more robust, performant, and scalable components. As a prominent example, quantum computing holds the potential to solve computational problems intractable for classical computers and advance healthcare, energy, climate, finance, and cybersecurity. However, the algorithmic complexity, finite qubit coherence, and imperfect control require quantum computers to scale to millions of physical qubits while maintaining low hardware error rates to impact real-world applications, necessitating quantum error correction and fast, high-fidelity, and simultaneous readout of a large number of qubits in each error correction cycle.

Quantum amplifiers are a critical frontend quantum hardware to faithfully amplify single-photon-level readout signals above the orders of magnitude larger ambient and electronics noise at room temperature. However, existing quantum amplifiers face performance-scalability tradeoff and are thus challenging to meet the demands of large-scale information-critical quantum systems. This thesis aims to develop next-generation quantum amplifiers that achieve optimal noise performance, scalability, directionality, and processor integrability at the same time. We invent a new class of amplifiers, Floquet-mode traveling-wave parametric amplifiers (TWPAs), that solves the long-standing performance-scalability tradeoff and theoretically offer broadband directional amplification with over 99.9% quantum efficiency across a wide bandwidth. Furthermore, we experimentally demonstrate a low-loss Floquet TWPA using our recently developed planar implementation architecture, offering advantages such as 100x less measured material loss than conventional methods and compatibility with aluminum superconducting qubit fabrication. This architecture will enable direct on-chip integration of quantum amplifiers with superconducting quantum processors, reducing hardware infrastructure overhead and energy dissipation of large quantum systems. In addition, in our quest for ideal quantum amplifiers, we develop a general broadband isolation scheme, in conjunction with our Floquet TWPA implementation, as a promising avenue towards realizing nonreciprocal broadband amplifiers, which will significantly improve system-level efficiency and unlock new opportunities in experimental science.

Thesis Committee:

Prof. Kevin P. O’Brien (Thesis Supervisor)

Prof. William D. Oliver

Prof. Karl K. Berggren

Details

• Date: Thursday, August 3
• Time: 2:00 pm - 3:30 pm
• Category: Thesis Defense
• Location: 34-401A (Grier A)

Additional Location Details:

Zoom Link: https://mit.zoom.us/j/97350841380?pwd=NFdmd1Awa2szSUJwWTBxQkJJZHR5dz09
Zoom meeting ID: 973 5084 1380
Zoom Password: TWPA