We propose a method to suppress decoherence in entangled systems by applying the series of joint measurements. While the standard Quantum Zeno Effect approach can only compensate for the slow enough Hamiltonian dynamics of the quantum system, the characteristic frequencies of the thermal bath contacting system may be greater than the maximal achievable frequencies of measurements. In this case, they cannot cancel out non-Hamiltonian evolution leading to the decoherence. We propose to use entanglement between the qubits of a quantum register to mitigate the negative effects of the interaction with the thermal bath, even with the lower frequencies of measurement. We show that even though this protocol does not lead to a complete freezing of the initial state, it still allows effective preservation of the entanglement in the system.
We propose a method to suppress decoherence in entangled systems by applying the series of joint measurements. While the standard Quantum Zeno Effect approach can only compensate for the slow enough Hamiltonian dynamics of the quantum system, the characteristic frequencies of the thermal bath contacting system may be greater than the maximal achievable frequencies of measurements. In this case, they cannot cancel out non-Hamiltonian evolution leading to the decoherence. We propose to use entanglement between the qubits of a quantum register to mitigate the negative effects of the interaction with the thermal bath, even with the lower frequencies of measurement. We show that even though this protocol does not lead to a complete freezing of the initial state, it still allows effective preservation of the entanglement in the system.
We apply the multiple, equally spaced in time, weak measurements, to the two-qubit entangled system to decrease the rate of its decoherence, i.e., to prevent the decrease of the off-diagonal elements. The scheme is similar to the Quantum Zeno Effect, but differs by the frequency of the measurements. While the conventional Quantum Zeno Effect assumes rapid measurements which mitigates the Hamiltonian dynamics, the proposed method makes use of entanglement between the qubits to decrease the decoherence rate. We will show that it allows us to partially suppress the decoherence in the case of Lindblad evolution.
Control of decoherence in open quantum systems has become a topic of great interest due to the emergence of quantum technologies that depend on quantum coherent effects. In this work, we investigate the decoherence dynamics of systems coupled to multiple baths through noncommuting systems' operators, and beyond the weak system-bath coupling limit. By building on cooperative effects between baths, we propose a novel strategy to mitigate rapid decoherence. Concretely, we study the dynamics of a qubit coupled to multiple environments with arbitrary interaction strengths, and along different coordinates. Based on insights gained on the decoherence dynamics from the analytical Effective Hamiltonian method, we carry out numerical simulations using the Reaction Coordinate quantum master equation method. In contrast to standard expectations, we show that when the system strongly interacts with a decohering bath, increasing its coupling to a second, dissipative bath slows down the decoherence dynamics. Our work offers insights into the preservation of quantum coherences in open quantum systems based on frustration effects, by utilizing cooperative effects between different heat baths.
We evaluate a discrete entanglement-protection protocol for a Bell two-qubit pair undergoing unitary evolution with a single mid-sequence phase change. The test circuit consists of state preparation, a phase shift that does not affect entanglement and emulates a useful quantum gate, and a final standard readout. We compare two variants over a total evolution time of 16 arbitrary time intervals: in the first variant, the phase operation is bracketed by two blocks of five two-qubit QND measurements without readout, while in the baseline variant these measurements are absent. Performance is quantified by the fidelity F, based on the concurrence metric; we take as the minimally acceptable lower bound, below which hardware noise can no longer be safely compensated by the available specialized tools. Simulations show that the protected scheme maintains throughout the entire observation window, whereas the unprotected scheme, under free evolution in realistic noise regimes encountered in experiments, quickly drops below this threshold even before the gate is applied. These results demonstrate that repeated projective measurements of the entangled state in the Bell basis, implemented as discrete quantum non-demolition (QND) two-qubit measurements without readout, substantially slow the loss of entanglement despite coupling to a thermal bath. The protocol requires fewer measurements, distinguishing it from high-frequency schemes that rely on the Zeno effect. The approach is directly relevant for fine-tuning superconducting and trapped-ion processors, for pure-state engineering, and for optimizing protocols that use mixed entangled input states. In particular, in these architectures the protocol naturally integrates with existing QND procedures and phase control, providing a means to curb decoherence. Practically, this implies periodic in-operation measurements every 1–2 arbitrary time steps, as well as the possibility of scaling to multi-qubit modules with improved gate fidelities and simplified calibration.
The Zeno and anti-Zeno effects are features of measurement-driven quantum evolution where frequent measurement inhibits or accelerates the decay of a quantum state. Either type of evolution can emerge depending on the system-environment interaction and measurement method. In this experiment, we use a superconducting qubit to map out both types of Zeno effect in the presence of structured noise baths and variable measurement rates. We observe both the suppression and acceleration of qubit decay as repeated measurements are used to modulate the qubit spectrum causing the qubit to sample different portions of the bath. We compare the Zeno effects arising from dispersive energy measurements and purely dephasing "quasimeasurements," showing energy measurements are not necessary to accelerate or suppress the decay process.
In this paper, we consider the dynamics of a system coupled to a thermal bath, going beyond the standard two-level system through the addition of an energy excitation degree of freedom. Further extensions are to systems containing many fermions, with the master equations modified to take Fermi-Dirac statistics into account, and to potentials with a time-dependent bias that induce resonant avoided crossing transitions. The limit $\stackrel{\ensuremath{\rightarrow}}{Q}\ensuremath{\infty},$ where the interaction rate with the bath is much greater than all free oscillation rates for the system, is investigated. Two behaviors are possible: freezing (quantum Zeno effect) or synchronization (motional narrowing). We clarify the conditions that give rise to each possibility, making an explicit connection with quantum-measurement theory. We compare the evolution of quantal coherence for the two cases as a function of Q, noting that full coherence is restored as $\stackrel{\ensuremath{\rightarrow}}{Q}\ensuremath{\infty}.$ Using an extended master equation, the effect of system-bath interactions on entanglement in bipartite system states is computed. In particular, we show that the sychronization case sees bipartite system entanglement fully preserved in the large Q limit.
We examine the appearance of Zeno and anti-Zeno effects (Misra and Sudarshan 1977 J. Math. Phys. 18 756; Kofman and Kurizki 2000 Nature 405 546; Kofman and Kurizki 1996 Phys. Rev. A 54 3750; Facchi et al 2001 Phys. Rev. Lett. 86 2699) in the entanglement dynamics of two qubits off-resonantly coupled to the same lossy cavity when the unitary evolution of the system is interrupted by repeated projective measurements. We describe in detail these quantum effects by comparing the measurement-induced coarse-grained dynamics to the entanglement evolution in the absence of measurements in several scenarios (Francica et al 2009 Phys. Rev. A 79 032310). In particular, we examine the strong and weak coupling regimes, the role of the relative coupling strengths between the two qubits and the reservoir and the effect of the detuning from the main cavity frequency. We show that the anti-Zeno effect can occur in the entanglement dynamics when the qubit frequencies are detuned from the main reservoir frequency. Furthermore, we find that Zeno and anti-Zeno effects can even appear sequentially many times as a function of the interval between the measurements. Finally, we show that, in the off-resonant regime, we can preserve the entanglement using the quantum Zeno effect more efficiently than in the resonant limit (Maniscalco et al 2008 Phys. Rev. Lett. 100 090503), even if, in this case, no sub-radiant state exists.