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There are other methods to reduce decoherence, but it is believed that QEC will be present in any QC. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle generation associated with absorption of γ-rays and cosmic-ray muons in the qubit substrate. Quantum Error Correction: the best hope for success. Here we characterize a superconducting multiqubit circuit and find that charge noise in the chip is highly correlated on a length scale over 600 micrometres moreover, discrete charge jumps are accompanied by a strong transient reduction of qubit energy relaxation time across the millimetre-scale chip. Another crucial requirement is that errors cannot be correlated. The goal here is to develop a theory of quantum error correction that takes into account correlated coherent errors and, in particular to deal with errors. Although the Heisenberg uncertainty principle precludes simultaneous monitoring of X- and Z-flips on a single qubit, it is possible to encode quantum information in large arrays of entangled qubits that enable accurate monitoring of all errors in the system, provided that the error rate is low 1. Unlike classical bits, which are susceptible to only one type of error, quantum bits (qubits) are susceptible to two types of error, corresponding to flips of the qubit state about the X and Z directions. A method, apparatus and product includes obtaining a logical representation of a quantum circuit and selecting a quantity of physical qubits for a physical representation of the quantum circuit, wherein the selecting of the quantity is based on a utility per-qubit metric that is used to define a utility per-qubit score of the quantum circuit. The central challenge in building a quantum computer is error correction.