To go more in depth into the working principles of transmon qubits, we invite you to read the following references:

The standard theory reference
J. Koch, et al., Charge-insensitive qubit design derived from the Cooper pair box, Physical Review A 76, 042319 (2007).

The standard experimental reference
J. A. Schreier, et al., Suppressing charge noise decoherence in superconducting charge qubits, Physical Review B 77, 180502 (2008).

Two very accessible blog articles by C. Dickel
How to make artificial atoms out of electrical circuits – part 1
How to make artificial atoms out of electrical circuits – part 2

Individually gating same-frequency qubits
S. Asaad, C. Dickel, N. K. Langford, S. Poletto, A. Bruno, M. A. Rol, D. Deurloo, and L. DiCarlo, Independent, extensible control of same-frequency superconducting qubits by selective broadcasting, NPJ Quantum Information 2, 16029 (2016).

Circuit QED architecture
A. Blais, R. S. Huang, A. Wallraff, S. M. Girvin, and R. J. Schoelkopf, Cavity quantum electrodynamics for superconducting electrical circuits: An architecture for quantum computation, Physical Review A 69, 062320 (2004).

Surface coding
A. G. Fowler, M. Mariantoni, J. M. Martinis, and A. N. Cleland, Surface codes: Towards practical large-scale quantum computation, Physical Review A 86, 032324 (2012).

For further details into the approach used in Professor Dicarlo’s lab for building surface-code quantum harware using an 8-qubit unit cell
R. Versluis, S. Poletto, N. Khammassi, B. Tarasinski, N. Haider, D. J. Michalak, A. Bruno, K. Bertels, and L. DiCarlo, Scalable quantum circuit and control for a superconducting surface code, Physical Review Applied 8, 034021 (2017).