Characterizing Superconducting Qubits Using Pulse-level Control
Open Access
- Author:
- Mc Millan, Marquis
- Area of Honors:
- Physics
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Nitin Samarth, Thesis Supervisor
Richard Wallace Robinett, Thesis Honors Advisor - Keywords:
- quantum computing
quantum
computing
qubits
superconductivity
superconducting
josephson-junction
josephson
junction
physics
transmon
IBM
rabi
oscillations
rabi oscillations
probability coefficient
simulation
eigen energy
eigen states
light
matter
interaction
field strength
remote experiment
python
scipy
numpy
cooper pair box
model
theoretical
characterizing
microwaves
pulse-level
control
spectroscopy - Abstract:
- First mentioned by Richard Feynman in 1981, quantum computers that aim to achieve efficient quantum simulations to solve quantum problems are now being developed in laboratories worldwide, thus making Feynmans scientific dream a life-changing reality. However, we might ask: "why not perform quantum simulations on our classical computers?" While classical computers are limited to binary-bits, quantum computers rely on entanglement and superpositions of quantum-bits (qubits) to execute calculations. This increases the computational power of a quantum computer because of its ability to analyze complex entangled systems in a superposition of states. The state of a qubit is represented as the superposition of the basis states of a two level quantum system. Quantum states are prepared by performing operations on qubits that are referred to as ‘quantum-gates’ and are the key component to all quantum computing operations. Our goal in this thesis was to use the IBM-Q platform to carry out experiments characterizing the transmon, a type of superconducting qubit that is derived from the Josephson-junction. A Josephson-junction consists of two superconductors separated by an insulator; this leads to a non-linear energy spectrum in the transmon that causes it to deviate from an evenly spaced energy spectrum (such as the quantum harmonic oscillator). We begin by modeling the transmon Hamiltonian by plotting the eigenvalues for an array of circuit parameters. Modeling the transmon Hamiltonian provides a deeper understanding into the quantization of a transmon. In comparison to the quantum harmonic oscillator, the transmon has a non-linear energy difference between each state. This enables the first two energy levels of our transmon to be the computational zero and one states. Consequently, the transmon has low charge sensitivity making it reliable under most circuit parameters. For experimentally accessible circuit parameters, the energy difference between the lowest two levels exist in the microwave regime. Therefore, qubit states are prepared by applying microwave pulses accessed through the IBMQ OpenPulse platform. We mapped the fundamental frequency of the qubit by driving microwave pulses with an array of frequencies and measuring the qubit response. Characterization through OpenPulse is a stepping-stone for cloud-based systems and tests the limits of contactless-quantum computation. Finally, we theoretically study the physics of light-matter interactions of an ideal two-level system, and compare the experimentally measured transmon response to on-resonant and off-resonant microwave radiation to the expected model. At low drive amplitudes, the experiments demonstrate an agreement with the expected dependencies, but deviate at stronger amplitudes. In this context, we study the impact of pulse rise-fall envelopes on the qubit response.