Browsing by Author "McCord, John J."

Now showing 1 - 4 of 4

Coherent interaction-free detection of microwave pulses with a superconducting circuit
(2022-12) Dogra, Shruti; McCord, John J.; Paraoanu, Gheorghe Sorin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The interaction-free measurement is a fundamental quantum effect whereby the presence of a photosensitive object is determined without irreversible photon absorption. Here we propose the concept of coherent interaction-free detection and demonstrate it experimentally using a three-level superconducting transmon circuit. In contrast to standard interaction-free measurement setups, where the dynamics involves a series of projection operations, our protocol employs a fully coherent evolution that results, surprisingly, in a higher probability of success. We show that it is possible to ascertain the presence of a microwave pulse resonant with the second transition of the transmon, while at the same time avoid exciting the device onto the third level. Experimentally, this is done by using a series of Ramsey microwave pulses coupled into the first transition and monitoring the ground-state population.
Coherent interaction-free detection of noise
(2024-09) McCord, John J.; Dogra, Shruti; Paraoanu, Gheorghe Sorin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The measurement and characterization of noise is a flourishing area of research in mesoscopic physics. In this work, we propose interaction-free measurements as a noise-detection technique, exploring two conceptually different schemes: the coherent and the projective realizations. These detectors consist of a qutrit whose second transition is resonantly coupled to an oscillatory field that may have noise in amplitude or phase. For comparison, we consider a more standard detector previously discussed in this context: a qubit coupled in a similar way to the noise source. We find that the qutrit scheme offers clear advantages, allowing precise detection and characterization of the noise, while the qubit does not. Finally, we study the signature of noise correlations in the detector's signal.
High-fidelity robust qubit control by phase-modulated pulses
(2024-01) Kuzmanović, Marko; Björkman, Isak; McCord, John J.; Dogra, Shruti; Paraoanu, Gheorghe Sorin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We present a set of robust and high-fidelity pulses that realize paradigmatic operations such as the transfer of the ground state population into the excited state and arbitrary X/Y rotations on the Bloch sphere. These pulses are based on the phase modulation of the control field. We provide an experimental proof-of-concept of these operations by using a transmon qubit, demonstrating resilience against deviations in the drive amplitude of more than ≈20%, and/or detuning from the qubit transition frequency in the order of 10MHz. This modulation scheme is straightforward to implement in practice and can be deployed to any other qubit-based experimental platform.
Theory of coherent interaction-free detection of pulses
(2023-07) McCord, John J.; Dogra, Shruti; Paraoanu, Gheorghe Sorin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Quantum physics allows an object to be detected even in the absence of photon absorption, by the use of so-called interaction-free measurements. We provide a formulation of this protocol using a three-level system, where the object to be detected is a pulse coupled resonantly into the second transition. In the original formulation of interaction-free measurements, the absorption is associated with a projection operator onto the third state. We perform an in-depth analytical and numerical analysis of the coherent protocol, where coherent interaction between the object and the detector replaces the projective operators, resulting in higher detection efficiencies. We provide approximate asymptotic analytical results to support this finding. We find that our protocol reaches the Heisenberg limit when evaluating the Fisher information at small strengths of the pulses we aim to detect - in contrast to the projective protocol that can only reach the standard quantum limit. We also demonstrate that the coherent protocol remains remarkably robust under errors such as pulse rotation phases and strengths, the effect of relaxation rates and detunings, as well as different thermalized initial states.