Speaker
Description
Environmental interactions are usually associated with decoherence and the loss of quantum information. However, they also play an essential role in the measurement, control, and stabilisation of quantum devices. We theoretically investigate this dual role in two open quantum systems.
The first system is a singlet–triplet qubit in a double quantum dot monitored by a quantum point contact. Standard descriptions of Pauli-spin-blockade readout typically assume a single electronic level per dot [1–3]. In this regime, the quantum point contact (QPC) acts as a nearby charge sensor. The counting statistics of the QPC current provides a clear readout contrast: the singlet branch produces noisy, super-Poissonian current, while the Pauli-blocked triplet branch remains approximately Poissonian. We extend this model by including a higher-energy electronic level. This additional level opens a leakage pathway that allows the triplet state to bypass Pauli spin blockade, reducing the fidelity of spin-to-charge conversion. At high QPC bias or small level splitting, this leakage produces strong bunching and super-Poissonian fluctuations in the triplet signal, so that the triplet branch can become noisier than the singlet. For larger level splittings or lower bias, the leakage is suppressed and the conventional readout regime is recovered. These results identify higher-level leakage as an important error mechanism in QPC-based spin readout and provide guidance for optimising bias, tunnel couplings, and level structure in semiconductor quantum devices.
The second system consists of two bosonic modes, each coupled to its own
independent bath. Motivated by the weak-coupling limitations on bosonic
autonomous entanglement engines identified in Ref. [4], we study whether
stronger and more general system–bath coupling can generate steady-state
entanglement autonomously. Using a non-equilibrium Green’s function approach, we go beyond Markovian weak-coupling treatments and include non-Markovian noise, strong bath coupling, and counter-rotating interaction terms which are neglected in the weak-coupling theory. The resulting logarithmic negativity shows that tailored dissipative environments can generate and stabilise entanglement in regimes that are inaccessible to weak-coupling theory.
Together, these studies show that the environment is not only a source of decoherence. When modeled as part of the device, environmental interactions can reveal new error mechanisms, define useful operating regimes, and provide resources for quantum readout and autonomous entanglement generation.
References
[1] S. D. Barrett and T. M. Stace, Phys. Rev. B 73, 075324 (2006).
[2] Ł. Marcinowski, K. Roszak, P. Machnikowski, and M. Krzyżosiak, Phys. Rev. B 88, 125303 (2013).
[3] K. Roszak, Ł. Marcinowski, and P. Machnikowski, Phys. Rev. A 91, 032118 (2015).
[4] B. Longstaff, M. G. Jabbour, and J. B. Brask, Phys. Rev. A 108, 032209 (2023).