Microwave Photon-Mediated Interactions between Semiconductor Qubits

Abstract

The realization of a coherent interface between distant charge or spin qubits in semiconductor quantum dots is an open challenge for quantum information processing. Here we demonstrate both resonant and non-resonant photon-mediated coherent interactions between double quantum dot charge qubits separated by several tens of micrometers. We present clear spectroscopic evidence of the collective enhancement of the resonant coupling of two qubits. With both qubits detuned from the resonator we observe exchange coupling between the qubits mediated by virtual photons. In both instances pronounced bright and dark states governed by the symmetry of the qubit-field interaction are found. Our observations are in excellent quantitative agreement with masterequation simulations. The extracted two-qubit coupling strengths significantly exceed the linewidths of the combined resonator-qubit system. This indicates that this approach is viable for creating photon-mediated twoqubit gates in quantum dot based systems.Semiconductor nanostructure based systems are one of the promising contenders for quantum information processing since they offer flexibility in tuning, long coherence times and well-established fabrication techniques [1,2]. However, scaling to larger numbers of qubits remains a challenge, since many coupling mechanisms for realizing two-qubit gates are short range, i.e. limited to nearest neighbors. For scaling to larger systems and eventually to a full scale quantum computer, a combination of short and longer range interactions seems promising [3].So far, short range (∼ 100 nm) qubit-qubit interaction has been realized via capacitive or exchange coupling between charge [4-6] and spin qubits [7-10], which was expanded by making use of interactions mediated by additional qubits (∼ 400 nm) [11] or electronic cavities (∼ 1.7 µm) [12]. However, it is predicted that the range of interaction between semiconductor qubits can be increased significantly using microwave photons [3,13,14]. A key ingredient, the strong coupling of individual charges [15,16] or spins [17][18][19] to individual microwave photons, has recently been realized in semiconductor implementations of circuit quantum electrodynamics (QED) [20].Here, we present experiments in which the coherent photon-mediated coupling between two spatially separated semiconductor qubits is realized both in the resonant and the dispersive regime using high impedance SQUID array resonators. The high Josephson inductance of the SQUID array increases the strength of the vacuum fluctuations of the electric field, enhancing the coupling strength of the individual qubits to the resonator [16] and consequently the qubitqubit coupling, which allows us to overcome the limitations of prior experiments [17,21,22]. This key step holds the strong promise that two-qubit gates based on photon-mediated interactions, which are a corner-stone in quantum information processing with superconducting circuits [23], are implementable with semiconductor qubits based on a variety of material systems. ...

Programable two-qubit gates in capacitively coupled flopping-mode spin qubits

“…Analogously to these exemplary two-qubit gates, the other quantum gates can also be realized with a fidelity close to 95%. These values can easily increase with a more optimistic choice of the pure dephasing rates, as observed in other similar experiments [28].…”

“…The two-qubit gates are often the most challenging since they require coupling between qubits. A wide variety of coupling types, from direct electron-electron interactions [2,[11][12][13][14][15][16][17][18][19][20][21][22] to interactions mediated by the substrate or other intermediate system [23][24][25][26][27][28][29], have been demonstrated for qubits defined in semiconductor quantum dots (QDs). The first type of coupling schemes, including capacitive coupling and exchange, are usually short range and would constitute the fundamental ingredient for qubit operations within a quantum computer node.…”

Semiconductor quantum computation

“…Since 2016, the strong coupling of a resonator to a DQD in the Si/SiGe heterostructure [129], the GaAs/AlGaAs heterostructure [130] and the carbon nanotube [131] have been reported successively. Upon these results, in 2018, Nicolí et al [132] demonstrated tunable photon-mediated coupling of two charge qubits and measured the two-qubit coupling strength. In the meanwhile, Scarlino et al [133] also demonstrated coherent coupling between a semiconductor charge qubit and a superconductor qubit, and even observed controlled oscillations.…”

Resonant microwave-mediated interactions between distant electron spins

“…In order to coherently couple spin qubits via cavity photons [21,22], it is necessary to bring the qubits into resonance with each other (virtual coupling), or into resonance with each other and the microwave cavity (resonant coupling). Unlike charge qubits, whose energy splittings can easily be electrically tuned [8], spin qubits confined in quantum dots have limited electrical tunability. Their energies are set by a total magnetic field B tot , which results from the vector addition of a global external field B ext and stray fields from micromagnets B M deposited on-chip to facilitate spin-photon coupling [18,23].…”