Noise Spectroscopy Using Correlations of Single-Shot Qubit Readout

A better understanding of the noise causing qubit decoherence is crucial for improving qubit performance. The noise spectrum affecting the qubit may be extracted by measuring dephasing under the application of pulse sequences but requires accurate qubit control and sufficiently long relaxation times, which are not always available. Here, we describe an alternative method to extract the spectrum from correlations of single-shot measurement outcomes of successive free induction decays. This method only requires qubit initialization and readout with a moderate fidelity and also allows independent tuning of both the overall sensitivity and the frequency region over which it is sensitive. Thus, it is possible to maintain a good detection contrast over a very wide frequency range. We discuss using our method for measuring both $1/f$ noise and the fluctuation spectrum of the nuclear bath of GaAs spin qubits.Comment: 5 pages, 3 figure

Institutionalized Bailouts and Fiscal Policy: The Consequences of Soft Budget Constraints

States have soft budget constraints when they can expect a bailout by the federal government in the event of a financial crisis. This gives rise to incentives for unsound state fiscal policy. We test whether states with softer budget constraints have higher debt and deficits, receive more bailouts funds, spend funds less efficiently, and are more likely to allocate funds to programs benefiting special interests. Exogenous variation in soft budget constraints across states and over time allows the identification of budget constraint softness on state fiscal policy. We take advantage of the fact that in Germany, states’ political influence is exogenous because voting weights differ in the upper chamber of the German parliament. The stronger the political influence of states, the softer their budget constraints. We show that states with softer budget constraint have higher deficits and debts, and receive more bailouts funds. Further, overrepresented states are less efficient in spending public funds and are more prone to respond to rent seeking by interest groups.