Enhanced energy relaxation process of a quantum memory coupled to a superconducting qubit (original) (raw)

Dynamical decoupling of superconducting qubits

Journal of Physics: Conference Series, 2012

We show that two superconducting qubits interacting via a fixed transversal coupling can be decoupled by appropriately-designed microwave field excitations applied to each qubit. This technique is useful for removing the effects of spurious interactions in a quantum processor. We also simulate the case of a qubit coupled to a two-level system (TLS) present in the insulating layer of the Josephson junction of the qubit. Finally, we discuss the qubit-TLS problem in the context of dispersive measurements, where the qubit is coupled to a resonator.

A superconducting quantum memory with tens of milliseconds coherence time

arXiv (Cornell University), 2023

Storing quantum information for an extended period of time is essential for running quantum algorithms with low errors. Currently, superconducting quantum memories have coherence times of a few milliseconds, and surpassing this performance has remained an outstanding challenge. In this work, we report a single-photon qubit encoded in a novel superconducting cavity with a coherence time of 34 ms, representing an order of magnitude improvement compared to previous demonstrations. We use this long-lived quantum memory to store a Schrödinger cat state with a record size of 1024 photons, indicating the cavity's potential for bosonic quantum error correction.

12 Dynamical decoupling of superconducting qubits

2016

Dissipative dynamics of superconducting hybrid qubit systems

Journal of Physics: Conference Series, 2009

We perform a theoretical study of composite superconducting qubit systems for the case of a coupled qubit configuration based on a hybrid qubit circuit made of both charge and phase qubits, which are coupled via a σx ⊗ σz interaction. We compute the system's eigen-energies in terms of the qubit transition frequencies and the strength of the inter-qubit coupling, and describe the sensitivity of the energy crossing/anti-crossing features to such coupling. We compute the hybrid system's dissipative dynamics for the cases of i) collective and ii) independent decoherence, whereby the system interacts with one common and two different baths of harmonic oscillators, respectively. The calculations have been performed within the Bloch-Redfield formalism and we report the solutions for the populations and the coherences of the system's reduced density matrix. The dephasing and relaxation rates are explicitly calculated as a function of the heat bath temperature.

Suppressing relaxation in superconducting qubits by quasiparticle pumping

Science (New York, N.Y.), 2016

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to reducing errors: Instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. In the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. A 70% reduction in the quasiparticle density results in a threefold enhancement in qubit relaxation times and a comparable reduction in coherence variability.

Superconducting Qubits: A Short Review

Cornell University - arXiv, 2004

Superconducting qubits are solid state electrical circuits fabricated using techniques borrowed from conventional integrated circuits. They are based on the Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit element available at low temperature. In contrast to microscopic entities such as spins or atoms, they tend to be well coupled to other circuits, which make them appealling from the point of view of readout and gate implementation. Very recently, new designs of superconducting qubits based on multi-junction circuits have solved the problem of isolation from unwanted extrinsic electromagnetic perturbations. We discuss in this review how qubit decoherence is affected by the intrinsic noise of the junction and what can be done to improve it.

Tunable Coupling of Superconducting Qubits

Physical Review Letters, 2003

We study an LC-circuit implemented using a current-biased Josephson junction (CBJJ) as a tunable coupler for superconducting qubits. By modulating the bias current, the junction can be tuned in and out of resonance and entangled with the qubits coupled to it. One can thus implement two-qubit operations by mediating entanglement. We consider the examples of CBJJ and chargephase qubits. A simple recoupling scheme leads to a generalization to arbitrary qubit designs.

Environmentally-induced Rabi oscillations and decoherence in superconducting phase qubits

Physical Review B, 2009

We study decoherence effects in a dc SQUID phase qubit caused by an isolation circuit with a resonant frequency. The coupling between the SQUID phase qubit and its environment is modeled via the Caldeira-Leggett formulation of quantum dissipation/coherence, where the spectral density of the environment is related to the admittance of the isolation circuit. When the frequency of the qubit is at least two times larger than the resonance frequency of the isolation circuit, we find that the decoherence time of the qubit is two orders of magnitude larger than the typical ohmic regime, where the frequency of the qubit is much smaller than the resonance frequency of the isolation circuit. Lastly, we show that when the qubit frequency is on resonance with the isolation circuit, an oscillatory non-Markovian decay emerges, as the dc SQUID phase qubit and its environment self-generate Rabi oscillations of characteristic time scales shorter than the decoherence time. PACS numbers: 74.50.+r, 85.25.Dq, 03.67.Lx

A long-lived memory qubit on a low-decoherence quantum bus

2007

We demonstrate long-lived coherence in internal hyperfine states of a single 43 Ca + trapped-ion qubit [T2 = 1.2(2) s], and in external motional states of a single 40 Ca + trapped-ion qubit [T ′ 2 = 0.18(4) s], in the same apparatus. The motional decoherence rate is consistent with the heating rate, which was measured to be 3(1) quanta/sec. Long coherence times in the external motional states are essential for performing high-fidelity quantum logic gates between trapped-ion qubits. The internal-state T2 time that we observe in 43 Ca + , which has not previously been used as a trapped-ion qubit, is about one thousand times longer than that of physical qubits based on 40 Ca + ions. Using a single spin-echo pulse to "re-phase" the internal state, we can detect no decoherence after 1 s, implying an effective coherence time T SE 2 > ∼ 45 s. This compares with timescales in this trap for single-qubit operations of ∼ 1 µs, and for two-qubit operations of ∼ 10 µs.

Enhanced energy relaxation process of a quantum memory coupled to a superconducting qubit (original) (raw)

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