Periodic Reporting for period 1 - MQC (Maintaining Quantum Coherence for Quantum Information Applications)
Período documentado: 2018-06-01 hasta 2020-05-31
made it possible to develop quantum architectures, such as trapped ions, color-defects in crystals (nitrogen-vacancy in
diamond), and Rydberg atoms, where quantum information applications can be implemented. At the heart of this growing
field stands quantum coherence.
In physics, coherence is maintained as long as waves preserve their relative phase, thus enabling the interference phenomenon. The same applies to quantum coherence, which is maintained when the quantum superposition (phase and amplitude) is kept stable. Quantum coherence is at the heart of quantum information technology. The latter can only be realised as long as quantum oherence is preserved. In fact, as quantum applications increase in complexity, coherence time needs to be extended. In a similar manner, longer coherence times reveal higher performance and higher quantum operation fidelity, which is important for ealizations of interesting quantum applications, varying from quantum gates for quantum computation, through quantum simulation of classical intractable systems, to quantum sensing schemes for medical applications.
Noise, leakage and decay channels constitute the main sources for decoherence, which limit the fidelity of the desired quantum operations. In this project my main goal is to theoretically investigate refocusing schemes to maintain coherence in the quantum systems mentioned above, while realizing different quantum applications:
In a theory-experiment collaboration with the Weizmann Institute group led by Ofer Firstenberg, we demonstrated that continuous dynamical decoupling can be applied to protect a collective excitation in warm atoms against Doppler broadening. When a photon (or a weak coherent pulse) is absorbed by atomic vapour, this global atomic excitation performs as a spin wave. Each atom possesses a phase according to its position, and the momentum of the absorbed photon. Due to random atomic velocities, the global excitation is subjected to Doppler decoherence that destroys the desired atomic phase. To tackle this, we introduce an additional ancillary sensor state, having an opposite sensitivity to the same Doppler mechanism. By smartly driving the transition between the excited and senor states, we couple them and obtain a protected dressed state that is insensitive to Doppler noise. The coherence time is prolonged. (Sent to publication in Phys. Rev. X)
The EU funding is acknowledged in all the articles published and will be acknowledged in future articles with the results of this research.
Our manuscript about the compensation for Doppler dephasing has been sent to publication in Phys. Rev. X, and has not been accepted yet. In addition to quantum memory application shown in our manuscript, our scheme can be used to increasing the entanglement gate fidelity of Rydberg atom architecture, which is currently, a less mature candidate for quantum computer in comparison with trapped ions and superconducting qubits. Moreover, our scheme is a new continuous dynamical decoupling scheme, which can be used for many other platforms, and against many other noise sources.