Non-destructive measurement of qbits Yale news "New qubit control bodes well for future of quantum computing" (Original paper) says:

"The Yale physicists successfully devised a new, non-destructive measurement system for observing, tracking and documenting all changes in a qubit’s state, thus preserving the qubit’s informational value."

Which would be the major applications of quantum theory that are impacted by this new technique? Wouldn't e.g. the security of quantum key distribution in cryptography be rendered
questionable?
 A: From the abstract of the original article (emphasis mine): 

Measuring a quantum system can randomly perturb its state. The strength and nature of this back-action depend on the quantity that is measured. In a partial measurement performed by an ideal apparatus, quantum physics predicts that the system remains in a pure state whose evolution can be tracked perfectly from the measurement record. We demonstrated this property using a superconducting qubit dispersively coupled to a cavity traversed by a microwave signal. The back-action on the qubit state of a single measurement of both signal quadratures was observed and shown to produce a stochastic operation whose action is determined by the measurement result. This accurate monitoring of a qubit state is an essential prerequisite for measurement-based feedback control of quantum systems.

That is, the abstract itself describes the fact that the measurement changes the state; what they are saying is that in their apparatus, how the state changes upon measurement of a subsystem can be reliably inferred from the measurement outcome, as in theoretical treatments of wave-function collapse of entangled states.
A: A "non-destructive measurement" is a highly misleading phrase in quantum mechanics experiments. A better (but less impressive) version is a "minimally perturbative measurement". In this and other papers, the claim is that researchers try to  perturb or change the system only as much as quantum mechanics requires. For superconducting qubits this is major progress: previous experiments tended to add far more noise that quantum mechanics required. There are many algorithms, including quantum error correction, which require a manipulate->measure->manipulate scheme at the quantum level.
Don't be misled by "New XXX bodes well for future of quantum computing" headlines. While this paper is important, the headline is used too often. 
