Principal Investigator: Prof. Chiranjib Mitra

Co-PI: Prof. T S Mahesh

The plan is to first identify and develop new materials which either have natural entanglement or where optically excited spin qubits can be generated and where it is possible to have entangled states in their excited states and one has to quantify the entanglement content. We have already achieved some expertise in this area where static entanglement quantification using magnetic susceptibility and heat capacity has been performed.

After this we intend to develop experimental techniques to perform spin dynamics which will be used to study entanglement dynamics as well as manipulation of spins for information processing. Techniques for spin dynamics will be developed to manipulate the spins and probe their spin coherence times. Decoherence of the electron spins is a major deterrent in using these materials for implementation of quantum gates and quantum bits (qubits). Improving coherence time and a technology to measure the coherence time faithfully will enable the device to have sufficient time available for the spin qubits to perform spin manipulation and have a better control for implementing various quantum gates.

Having obtained a handle on the mechanism of addressing the spin qubits we subsequently intend to develop quantum gates like the superposing Hadamard Gate and entangling Control‐NOT Gate which are the basic building blocks of a quantum information processing device. During this process a lot of electronics instrumentation and computer programming for interfacing and data processing needs to be done.

Principal Investigator: Prof. Subroto Mukerjee

Co-PIs: Prof. Sumilan Banerjee

In Many Body Localization (MBL) systems that are typically studied, the qubits are arranged along a line with interactions only between close neighbors although this is not essential for the techniques employed. The standard theoretical technique that is used is numerical exact diagonalization, usually of a system of about 12‐ 18 qubits to obtain all energy eigenstates or to evolve a given initial state. In the language of quantum computing, MBL systems are simply systems of several qubits coupled to each other in an architecture of random interactions in which it is possible to obtain the evolution of arbitrary initial states. This evolution is expected to result in very slow dephasing as mentioned earlier.

Of critical importance in harnessing the power of MBL for quantum storage and computation is quantifying the amount of dephasing as a function of time in terms of the interactions between the qubits. This is an issue that has so far not received much attention. Our primary goal is to quantify dephasing in these systems as a function of microscopic parameters in model Hamiltonians of MBL systems. Most studies of the evolution of initial states in MBL systems have so far focused on only lightly entangled initial states. We plan to study the evolution of initial states with various amounts of entanglements including Schrodinger cat states which are very important for quantum computation.

Diamond with NV centers has also emerged as a promising candidate for quantum computation. In this system the qubits interact with one another through dipolar interactions, which may appear random if they are distributed randomly inside the diamond crystal. Another example is deep levels in silicon where too qubits arranged at random interact with one another. Thus, the system we propose to study bears close resemblance to actual physical systems that are currently being studied intensely for their potential in quantum computing.

Principal Investigator: Prof. V. Praveen Bhallamudi

Co-PIs: Prof. Anil Prabhakar

Spin‐states associated with the negatively charged NV center in diamond have several properties that make them a leading quantum sensor, especially for magnetic sensing, for many applications that require high sensitivity and spatial resolution. The NV spins also provide one of the most promising platforms for room temperature quantum computation (QC). The project will have the following components:

1. Development of state‐of‐art NV‐spin based quantum measurement systems: Demonstration of single qubit coherent manipulation using quantum gates, demonstration of quantum register based on NV and coupled nuclear spins, implementation of quantum gates and multi‐qubit entanglement.

2. Development of NV sensor for magnetic resonance spectroscopy and imaging: Demonstration of high sensitivity agnetometry using coherent manipulation of single NV center, demonstration of spin‐relaxation based spectroscopy using NV centers and studying ferromagnetic resonance using it, development of novel platforms for diamond sensors to improve their applicability.

After building the experimental set‐up, we will first demonstrate the ability to address, initialize, coherently manipulate and measure a single NV qubit or sensor. We then aim to demonstrate a quantum register consisting of an NV spin along with the nuclear moments it is coupled to via hyperfine interaction. These will lead to demonstration of quantum gates that control both the NV and nuclear spins using resonant microwaves. We will aim to achieve multi‐qubit entanglement will be challenging within the 3 yr timeframe and may require the project to be extended to 5 years or more.

On the sensing side, we aim to demonstrate high sensitivity (few nT/√Hz) magnetometry using coherent manipulation of NV centers and employing using dynamic decoupling schemes. The schemes will be similar to those used for quantum computing work as well and the overlap should allow to make progress on both sensing and computation fronts simultaneously. We will use this magnetometry to measure magnetic resonance spectra of a nuclear and/or electron spin either within the diamond itself and/or outside of it. Our other focus in sensing work will be to further develop the recently demonstrated spectroscopy based on spin‐relaxation of NV centers by target spins. This is particularly useful in studying ferromagnetic and spinwave resonances. We aim to study dynamics and damping in ferromagnets, especially in recently discovered 2D ferromagnets, using NV centers. Finally, we will aim to develop new platforms for the NV sensors to improve their applicability. These will include a platform combining optics, magnetics and acoustics which can provide an energy efficient and miniaturized packaging for NV sensors. We also aim to investigate one based on nanodiamonds trapped in an optical tweezer. This can provide a control of the NV spins orientation and can be used as a probe that can be scanned relative to the sample for imaging.

In summary, diamond offers a great potential for scalable QC technology. We aim to bring our expertise in NV‐based and optical measurements to help develop such quantum computing and quantum sensing technologies in India.

Principal Investigator: Prof. Kasturi Saha

Co-PI: Prof. Sai Vinjanampathy

This project aims to build infrastructure for probing various types of colour centers in diamond such as nitrogen vacancies, silicon vacancies and germanium vacancies for quantum information and computation. The advantage of nitrogen and silicon vacancy centers is that multi‐qubit operations can be achieved using the isotopes of Nitrogen (N‐14, N‐15), Carbon (C‐13) and Silicon (Si‐29). The research will be focussed on building fabrication capabilities for design and fabrication of cavities which can be coupled to diamond emitters along with setting up measurement tools such as cryostat and confocal microscope for performing optically detected magnetic resonance (ODMR) experiments. The objectives would be to show single qubit performance that satisfies the Loss‐DiVincenzo’s criteria 6. The primary deliverables would be the realization of single qubit initialization and measurement protocols and implementation of single qubit and multi‐qubit gates. Using the initial experimental capabilities, generation and characterization of entangled states will be the next step. Finally the aim will be to extend the experimental capabilities for generating entanglement between distant locations.

Principal Investigator: Prof. T S Mahesh

Co-PI: Prof. Chiranjib Mitra

Over last two decades, nuclear spin ensembles in bulk samples manipulated by nuclear magnetic resonance (NMR) methods have proven to be a good testbed for studying the basic principles of various quantum phenomena. Although excellent controllability of nuclear spin dynamics allows high precision quantum operations, week sensitivity and low purity of quantum states have posed serious challenges on the scalability of the conventional NMR approach.

Superior sensitivity of optically detected magnetic resonance (ODMR) has led to a number applications from material characterization to quantum control. For example, optical pumping of spin levels in NV‐center (nitrogen‐vacancy center) defects in diamond allow efficient preparation of high purity quantum states. The NV center spin dynamics can be controlled via microwave pulses and even neighbouring nitrogen or carbon nuclear spins can be accessed via hyperfine interactions. Moreover, the quantum states of a single NV center can be measured optically, via fluorescence counts with the help of a confocal microscope. Since all these manipulations can be conveniently carried out even at ambient temperatures, NV‐centers promise toward a practical quantum device with a variety of applications such as imaging, field sensing, single‐photon emission, etc. A large scale engineered implantation of NV‐center defects in diamond is a challenge – which if overcome, can present new opportunities in multi‐qubit quantum processor working at ambient temperature.

Here we propose methodology developments in both single‐ and ensemble‐spin platforms based on both ODMR and NMR – relevant to quantum devices.

Principal Investigator: Prof. Kavita Dorai

Co-PI: Prof. Arvind

This project aims at new methods of suppressing quantum decoherence, designing highly accurate and fault‐tolerant quantum gates, protecting fragile computational resources such as multi‐qubit entangled states and performing simulations of quantum systems at the next level on an NMR quantum computer. The problems of low spin polarization, very little entanglement and small qubit registers will be tackled under the aegis of this project and we hope to push the boundaries of research in the field of magnetic resonance and design the next generation of NMR quantum computers. We propose using several sophisticated methods based on dynamical decoupling to decouple the system‐bath interactions and hence tackle the problem of suppressing quantum decoherence. This will help increase the lifetime of quantum states and enable the quantum computation to be performed efficiently, before the system decays. We also plan to increase the qubit register size (using different topologies and by using molecules with interactions specifically tailored for quantum computing) and thereby demonstrate important quantum algorithms such as Shor's quantum factoring algorithm and the quantum principal component analysis algorithm. An important component of this project is the simulation of quantum systems, including molecular Hamiltonians and performing quantum chemistry, on an NMR quantum computer. Another important component of this project is the use of machine learning approaches and genetic programming methods to achieve a high degree of quantum control.

Principal Investigator: Prof. Ritabrata Sengupta

Co-PI: Prof. Rohit Soni

1. The principal phenomenon, which differs quantum mechanics from classical mechanics is called entanglement. One reason why quantum computers are believed to be more efficient than its classical part is the use of entanglement in quantum algorithms.

2. To develop new methods for detection of entanglement for states in a bipartite (resp. multi‐partite) systems. This approach is based on positive maps. (Henceforth this objective will be identified and referred as B1)

3. To develop new measures of entanglement for such states. (Henceforth this objective will be identified and referred as B2).

4. The fundamental object in quantum communication theory are quantum protocols which are performed by quantum channels. Performance of channels can be quantified by channel capacity. However, even for the classical cases, calculating capacity of a generic channel is not easy. It turns out that capacity for quantum channels are enhanced by use of entangled states. This came as a surprise, as for a few channels, for which capacity could be calculated, quantum capacity turned out to be at best as the classical capacity. This was believed to be so for all channels. The mathematical reason for this phenomenon has not been well understood.

5. To study channel capacity and its application. (Henceforth this objective will be identified and referred as B3).

6. Most of the problems mentioned above are intrinsically related to the theory of majorisaion for matrices. This is a powerful tool which has been used in probability theory, martingale theory, information theory, systems and controls, game theory, and etc. to name a few. This naturally arises in the theory of converting one state to another. This also gives protocols so that one state can not be converted to another by local operations and classical communications, which in principle, can give potential methods for cryptography protocols. In this case we are dealing with infinite dimensional systems. Majorisation of such objects are not always studied. Nevertheless, if an infinite dimensional state has well defined second moments, then the covariance matrix with respect to position and momentum operators can be written. Such matrices are of finite dimensions. Study of majorisation in these context has become an important area of research in recent years. Hence the fourth aspect of this project is to study majorisation theory. (Henceforth this objective will be identified and referred as B4).

Principal Investigator: Prof. Rajesh V. Nair

The proposed project is intended to study the spontaneous emission of Nitrogen Vacancy (NV) centers or color centers in nanodiamonds in both frequency and time domain. The proposed project is not only important for the fundamental understanding of the physics of NV centers but may also help to improve the sensitivity of existing NV center based nano‐sensors and towards the realization of a room temperature quantum communication network.

Principal Investigator: Prof. A. R. Usha Devi

Co-PI: Prof. Sudha

We propose a series of coordinated investigations on some of the foundational aspects of quantum theory, which are identified to have direct implications on quantum technology innovations.

1. Uncertainty relations in the presence of multiple entangled memories.

2. Importance of incompatible measurements with an increase in the number of entangled memory systems.

3. Investigations on different forms of uncertainty relations, their inter‐connectivity, and their resource nature in developing and improving quantum inspired technology.

4. Enhancement of precision with control and feedback of measurements using quantum filtering theory.

Theoretical understanding of these concepts has direct impact in sustaining and supporting the modern quantum technological improvements. More specifically, quantification of key rate in quantum key distribution (QKD) is directly interlinked with uncertainty relations in the presence of a entangled memory. Incompatible measurements play an essential impact on uncertainty relations and hence on the key rate in QKD. Identifying improved security proofs and enhanced key rates using larger number of networked entangled memories and quantification of key rates in terms of relevant uncertainty relations proves to broaden the platform for QKD protocols.