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Novel architecture for building small scale quantum processors

Schematic of the “trimon” device consisting of four Josephson junctions and four capacitor pads implementing three longitudinally coupled qubits depicted as spins

Schematic of the “trimon” device consisting of four Josephson junctions and four capacitor pads implementing three longitudinally coupled qubits depicted as spins


A quantum computer, when realized, will provide exponential speedup compared to contemporary computers which follow the laws of classical physics. This will also enable a universal quantum simulator that can emulate real-world quantum systems that are otherwise intractable. A quantum bit or “qubit” is the basic building block of a quantum computer which exploits the properties of quantum mechanics like superposition (the ability of a qubit to be in two states at the same time) and quantum entanglement. Information processing using quantum mechanics requires precise control and manipulation of single-qubit, multi-qubit interactions as well as protection of the qubits from accidental measurement by the environment (quantum error). Among the various architectures being explored, superconducting circuits operating at millikelvin temperatures provide unparalleled flexibility in designing efficient quantum hardware.

The Quantum Measurement and Control (QuMaC) research group at TIFR has demonstrated a novel multimodal device implementing three strongly coupled qubits in a single circuit. As shown in the picture above, the device looks like a Wheatstone bridge with Josephson junctions replacing the resistors and capacitor pads connected to each node. The Josephson junctions function as lossless nonlinear inductors leading to three coupled anharmonic oscillator modes and each mode acts as a qubit. The strong, inter-qubit longitudinal coupling allows simple implementation of multi-qubit gate operations. The researchers have used this small three-qubit processor, named the “trimon”, to prepare entangled states and swap quantum information between qubit pairs. This design provides a new way of building multi-qubit systems and shows potential for various quantum information processing applications like quantum simulation, quantum error correction and quantum annealing.

Reference: Research article: “Implementation of Pairwise Longitudinal Coupling in a Three-Qubit Superconducting Circuit” by Tanay Roy, Suman Kundu, Madhavi Chand, Sumeru Hazra, N. Nehra, R. Cosmic, A. Ranadive, Meghan P. Patankar, Kedar Damle, and R. Vijay, Physical Review Applied 7 054025 (2017)

More details on the research group can be found here