def bare_spectrum(sweep, subsys, which=-1, **kwargs):
    """
    Plots energy spectrum of bare system `subsys` for given ParameterSweep `sweep`.

    Parameters
    ----------
    sweep: ParameterSweep
    subsys: QuantumSystem
    which: int or list(int), optional
        default: -1, signals to plot all wavefunctions within the truncated Hilbert space;
        int>0: plot wavefunctions 0..int-1; list(int) plot specific wavefunctions
    **kwargs: dict
        standard plotting option (see separate documentation)

    Returns
    -------
    fig, axes
    """
    subsys_index = sweep.get_subsys_index(subsys)
    specdata = sweep.bare_specdata_list[subsys_index]
    if which is None:
        which = subsys.truncated_dim
    return specdata.plot_evals_vs_paramvals(which=which, **kwargs)