Silicon spin qubits are a promising quantum computing platform offering long coherence times, small device sizes, and compatibility with industry-backed device fabrication techniques. In recent years, high fidelity single-qubit and two-qubit operations have been demonstrated in Si. Here, we demonstrate coherent spin control in a quadruple quantum dot fabricated using isotopically enriched 28 Si. We tune the ground state charge configuration of the quadruple dot down to the single electron regime and demonstrate tunable interdot tunnel couplings as large as 20 GHz, which enables exchange-based two-qubit gate operations. Site-selective single spin rotations are achieved using electric dipole spin resonance in a magnetic field gradient. We execute a resonant-CNOT gate between two adjacent spins in 270 ns.Quantum processors based on spins in semiconductors [1-3] are rapidly becoming a strong contender in the global race to build a quantum cofmputer. In particular, silicon is an excellent host material for spin-based quantum computing by virtue of its small spin-orbit coupling and long spin coherence times [4,5]. Within the past few years, tremendous progress has been made in achieving high fidelity single-qubit [6, 7] and two-qubit control [8][9][10][11][12] in silicon. Scalable one-dimensional arrays of silicon quantum dots have been demonstrated [13], and in GaAs, where electron wavefunctions are comparably large, both one-[14-16] and two-dimensional arrays [17,18] of spins have been fabricated. Despite this progress, quantum control of spins in silicon has been limited to one-and two-qubit devices. Scaling beyond two-qubit devices opens the door to important experiments which are currently out of reach, including error correction [19,20], quantum simulation [21][22][23][24], and demonstrations of time crystal phases [25].In this Letter, we demonstrate operation of a fourqubit device fabricated using an isotopically enriched 28 Si/SiGe heterostructure. The device offers independent control of all four qubits, as well as pairwise two-qubit gates mediated by the exchange interaction [26]. We demonstrate control and measurement of the charge state of the array, and operate in the regime where each dot contains only one electron. We perform electric dipole spin resonance (EDSR) spectroscopy on all four qubits to show that they have unique spin resonance frequencies. Finally, we modulate the tunnel coupling between adjacent dots and demonstrate a resonant-CNOT gate [9,27].Four spin qubits are arranged in a linear array using an overlapping gate architecture, as shown in Fig. 1(a) [28]. Single spin qubits are formed by accumulating a electron under each plunger gate: P 1 , P 2 , P 3 , and P 4 . The couplings between dots and between dots and the charge reservoirs formed beneath gates S 3 and D 3 are tuned by adjusting the barrier gate voltages V Bi . Charge sensing is performed by monitoring the currents I S1 and I S2 through two proximal quantum dot charge detectors TS 800 600 650 850 V P4 (mV) 640 700 800 Dot 4 V P1 (m...

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