Abstract: Microwave resonator readout of the cavity-spin interaction between a spin defect center ensemble and a microwave resonator yields fidelities that are orders of magnitude higher than is possible with optical readouts. In microwave resonator readout, microwave photons probe a microwave resonator coupled to a spin defect center ensemble subjected to a physical parameter to be measured. The physical parameter shifts the spin defect centers' resonances, which in turn change the dispersion and/or absorption of the microwave resonator. The microwave photons probe these dispersion and/or absorption changes, yielding a measurement with higher visibility, lower shot noise, better sensitivity, and higher signal-to-noise ratio than a comparable fluorescence measurement. In addition, microwave resonator readout enables coherent averaging of spin defect center ensembles and is compatible with spin systems other than nitrogen vacancies in diamond.

Abstract: Microwave resonator readout of the cavity-spin interaction between a spin defect center ensemble and a microwave resonator yields fidelities that are orders of magnitude higher than is possible with optical readouts. In microwave resonator readout, microwave photons probe a microwave resonator coupled to a spin defect center ensemble subjected to a physical parameter to be measured. The physical parameter shifts the spin defect centers' resonances, which in turn change the dispersion and/or absorption of the microwave resonator. The microwave photons probe these dispersion and/or absorption changes, yielding a measurement with higher visibility, lower shot noise, better sensitivity, and higher signal-to-noise ratio than a comparable fluorescence measurement. In addition, microwave resonator readout enables coherent averaging of spin defect center ensembles and is compatible with spin systems other than nitrogen vacancies in diamond.

Abstract: Microwave resonator readout of the cavity-spin interaction between a spin defect center ensemble and a microwave resonator yields fidelities that are orders of magnitude higher than is possible with optical readouts. In microwave resonator readout, microwave photons probe a microwave resonator coupled to a spin defect center ensemble subjected to a physical parameter to be measured. The physical parameter shifts the spin defect centers' resonances, which in turn change the dispersion and/or absorption of the microwave resonator. The microwave photons probe these dispersion and/or absorption changes, yielding a measurement with higher visibility, lower shot noise, better sensitivity, and higher signal-to-noise ratio than a comparable fluorescence measurement. In addition, microwave resonator readout enables coherent averaging of spin defect center ensembles and is compatible with spin systems other than nitrogen vacancies in diamond.

Abstract: Systems and methods for providing secure quantum digital signatures. In one embodiment, a digital signature user creates a plurality of identical “public” keys having one or more bits and a corresponding quantum mechanical one-way function. Quantum digital signature recipients use a “swap test” to check the validity of a copy of the key, and compare the test results with others. The quantum digital signature user sends a signed message over any channel, including an insecure channel. The recipients evaluate the signed message, and quantify the number of incorrect keys. The message is deemed valid and original, or forged and/or tampered with, when the number of incorrect keys is less than a lower threshold, or exceeds an upper threshold, respectively. For an intermediate number of incorrect keys, the recipients determine message authenticity by comparing observations. Hardware useful for application of the method is disclosed.

Abstract: Systems and methods for providing secure quantum digital signatures. In one embodiment, a digital signature user creates a plurality of identical “public” keys having one or more bits and a corresponding quantum mechanical one-way function. Quantum digital signature recipients use a “swap test” to check the validity of a copy of the key, and compare the test results with others. The quantum digital signature user sends a signed message over any channel, including an insecure channel. The recipients evaluate the signed message, and quantify the number of incorrect keys. The message is deemed valid and original, or forged and/or tampered with, when the number of incorrect keys is less than a lower threshold, or exceeds an upper threshold, respectively. For an intermediate number of incorrect keys, the recipients determine message authenticity by comparing observations. Hardware useful for application of the method is disclosed.

Abstract: An approach to processing quantum information uses a bulk ensemble of a very large number of identical entities as its source of quantum degrees of freedom. The information is represented as the deviation from uniform population probability for at least one of the quantum states of the ensemble. Coherences between quantum states, created when the ensemble is modified in a way that removes it from thermal equilibrium can serve as effective degrees of freedom. A bulk thermal ensemble of nuclear spins in a static magnetic field is treated using nuclear magnetic resonance pulses for preparation of an initial pure state, and effecting arbitrary single-spin and coupled multi-spin rotations. Readout of the result is accomplished by observation of the magnetization of the ensemble.