Protecting Quantum Spin Coherence of Nanodiamonds in Living Cells

Abstract

Due to its superior coherent and optical properties at room temperature, the nitrogen-vacancy (NV) center in diamond has become a promising quantum probe for nanoscale quantum sensing. However, the application of NV containing nanodiamonds to quantum sensing suffers from their relatively poor spin coherence times. Here we demonstrate energy efficient protection of NV spin coherence in nanodiamonds using concatenated continuous dynamical decoupling, which exhibits excellent performance with less stringent microwave power requirement. When applied to nanodiamonds in living cells we are able to extend the spin coherence time by an order of magnitude to the T1-limit of up to 30µs. Further analysis demonstrates concomitant improvements of sensing performance which shows that our results provide an important step towards in vivo quantum sensing using NV centers in nanodiamond.Introduction.-Nitrogen-Vacancy (NV) centers in diamond exhibit stable fluorescence and have a spin triplet ground state, which can be coherently manipulated by microwave fields [1]. Observation of spin-dependent fluorescence provides an efficient way to readout the spin state of NVs. The energy splitting of the NV spin depends on physical parameters, such as magnetic field [2-4], electric field [5, 6], temperature [7-10] and pressure [11,12]. A variety of quantum sensing protocols for precise measurement of these physical parameters in different scenarios have been developed [13][14][15][16][17][18][19][20][21][22]. These protocols are all based on determining the NV spin energy splitting, which is why the measurement sensitivity is limited by the NV spin coherence time.Spin coherence in bulk diamond is mainly affected by surrounding electronic impurities (P1 centers) and nuclear spins (natural abundance of 13 C isotope). The spin reservoir can be eliminated by using isotopically engineered high-purity type IIa diamond [23]. In order to mitigate the influence of any residual impurities, pulsed dynamical decoupling has been widely exploited to prolong spin coherence time [24][25][26]. Its excellent performance when applied to NVs in bulk diamond is a result of the quasi-static characteristics of the spin reservoir in bulk diamond and the high available microwave power. Unfortunately, these two factors may not be satisfied for NV centers in nanodiamonds, which are required for sensing applications in vivo. NVs contained within nanodiamonds typically exhibit poor spin coherence time, which has been attributed to nanodiamond surface spin noise and electric charge noise that include prominent high frequency components. Preserving the coherence of NVs in nanodiamonds becomes even more problematic

Is a Quantum Biosensing Revolution Approaching? Perspectives in NV‐Assisted Current and Thermal Biosensing in Living Cells

“…Even more complex dynamic decoupling sequences, which apply multiple refocusing pulses further improving the coherence time T 2 have been devised. [72][73][74][75] Among these, the most famous are the Carr-Purcell-Meiboom-Gill (CPMG) [72][73][74][75] and the XY8 sequences, [72,76] which differ in the rotation axes (around which the spin rotates): the first method applies the pulses along the same axis, while the second chooses a different one for each pulses. It is useful to underline that, although these techniques allow to extended the coherence time of the NV centers, they cannot go beyond the spin-lattice relaxation time T 1 , that for an NV spin ensemble in bulk diamond is about 3 ms. [77] Figure 2.…”

Shaped Pulses for Energy-Efficient High-Field NMR at the Nanoscale

“…To restore the NMR signal, high peak power and high average power should be delivered. Unfortunately high microwave power lead to heating effects especially in biological samples [35], and is difficult to achieve as microwave structures that deliver the control fields are limited in peak and average power.…”

“…Secondly, we present a solution to this problem based on suitable shaping of long πpulses which achieve an effective dynamics that has the same effect as an instantaneous π-pulse restoring the ideal sensortarget interaction. In this manner we can extend the duration of the π-pulses and reduce the required peak and average power to levels that are more accessible to current technology and compatible with sensing applications in biological samples [8,35]. Our protocol is universal and can be incorporated into any pulse sequence used in experiments to reduce microwave power consumption.…”

Temperature Selective Thermometry with Sub‐Microsecond Time Resolution Using Dressed‐Spin States in Diamond

“…In addition, because a continuous microwave is used, it is easy to measure the sample temperature as a function of microwave power before the experiment, and one can avoid damage to the biological tissue by setting the initial temperature of an incubator considering microwave heating. [ 50 ] The method is also expected to facilitate investigating the thermal properties of nanoelectronic devices where external magnetic fields fluctuate over time by the varying electric current. Therefore, the high temporal resolution and selective temperature sensitivity demonstrated here can be applied to the characterization of the transient thermal processes occurring in various nanoscale systems.…”