Fast control of dissipation in a superconducting resonator

Abstract

We report on fast tunability of an electromagnetic environment coupled to a superconducting coplanar waveguide resonator. Namely, we utilize a recently-developed quantum-circuit refrigerator (QCR) to experimentally demonstrate a dynamic tunability in the total damping rate of the resonator up to almost two orders of magnitude. Based on the theory it corresponds to a change in the internal damping rate by nearly four orders of magnitude. The control of the QCR is fully electrical, with the shortest implemented operation times in the range of 10 ns. This experiment constitutes a fast active reset of a superconducting quantum circuit. In the future, a similar scheme can potentially be used to initialize superconducting quantum bits.Tunable dissipative environments for circuit quantum electrodynamics (cQED) are pursued intensively in experiments due to the unique opportunities to study non-Hermitian physics 1,2 , such as phase transitions related to parity-time symmetry 3 , decoherence and quantum noise 4 . Interesting effects can be observed in experiments on exceptional points 5-7 , which also gives possibilities to use such systems as models in nonlinear photonics, for example, for metamaterials 8 and for photonic crystals 9 .From the practical point of view, tunable environments are utilized to protect and process quantum information 10-12 and to implement qubit reset 13,14 . The latter application calls for fast tunability of the environment due to the aim to increase the rate of the operations on a quantum computer. Recent advances in the field of cQED for quantum information processing 14-17 render this topic highly interesting.There are different ways for resetting superconducting qubits. Firstly, one may tune the qubit frequency to reduce its life time 18 . The disadvantages of this method include the broad frequency band reserved by the qubit and the required fast frequency sweep which may lead to an increased amount of initialization error 19 . Conventionally, it is beneficial to maintain the qubits at the optimal parameter points during all operations. Secondly, it is possible to use microwave pulses to actively drive the qubit to the ground state 20-23 . Such methods are popular because no additional components or new control steps are needed. However, to achieve high fidelity one usually needs to increase the reset time to the microsecond range. Thirdly, one can engineer a tunable environment for the qubits 13,24-26 . This approach demand changes in the chip design, but may lead to high fidelity for a fast reset without compromises on the other properties.Here, we focus on a single-parameter-controlled tunable environment implemented by a quantum-circuit refrigerator (QCR) 5,27-31 . The refrigerator is based on photonassisted electron tunneling through two identical normalmetal-insulator-superconductor junctions (NIS). It has been used to cool down a photon mode of the resonator 27 , and to observe a Lamb shift in a cQED system 31 . Furthermore, QCR can be used as a cryogenic photon source 29 , which ma...

Exceptional points in tunable superconducting resonators

“…The instantaneous response of the damping rates to the applied voltages shows that we can control the dissipation on a timescale substantially shorter than 1 μs. The QCR can be operated even at timescales in the range of 10 ns [63]. Furthermore, the dependence of the damping rate on the pulse amplitude follows the theory, as shown in the inset.…”

Tunable refrigerator for nonlinear quantum electric circuits

“…Note that since typically C tr is of the order of a few to several tens of fF, in designing the combined QCR-transmon system, it may be important to account for the coupling to the QCR, since in previous experiments C c ≈ 800 fF and C ≈ 10 fF [40,42,43,48]. With this notation, the Hamiltonian for the combined QCR-transmon system readŝ…”

“…[42], this model was found to describe accurately both the tunability of the resonator dissipation rate by orders of magnitude and the consequently induced Lamb shift of the resonance frequency. Reference [43] experimentally demonstrated that the QCR can be turned on/off in nanosecond time scale, which seems adequate for qubit initialization.…”

Hidden Chern number in one-dimensional non-Hermitian chiral-symmetric systems

“…Adding a non-Hermitian component to a Hamiltonian does not only broaden the resonances and allow the eigenstates to decay, but the eigenmodes can merge with each other at exceptional points, which are topological defects where not only the eigenvalues are degenerate but also the eigenvectors are parallel to each other [1,[12][13][14][15]. The flexibility to engineer gain and loss in a controllable manner for example in optics, (opto)mechanics, plasmonics, superconducting quantum circuits, dissipative Bose-Einstein condensates, exciton-polariton condensates and cold atom systems [1,2,12,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] have naturally raised the interest to study the symmetry and topology in non-Hermitian physics systematically [33][34][35][36][37] with potential applications for example in the design of topologically protected laser modes [38][39][40][41][42][43].…”