I'm currently halfway through my physics PhD, but I can't help but think I did this degree for the wrong reason: to break into a career that no longer appeals.
I thought I would find doing research really exciting and hugely rewarding. The problem is that I don't enjoy research after all, and I don't seem to be very good at it either. After almost 18 months, I feel like I'm just beginning to get to grips with my project, and I seem to have virtually no results.
I no longer want an academic career or even a research career. If I'm not going to work in these jobs, what is the point of having a PhD?
I'm now seriously considering walking away, but before I approach my supervisor I want an honest opinion on the impact of a "failed" PhD on my career prospects. I know he is going to try to talk me out of it and make out that I'm going to put a blight on my future.
If I do leave, how do I explain what I've been doing for the last year and a half? I've heard that you can convert a PhD to an MPhil -- should I look into this?
You are right in taking time to consider all the implications of quitting the programme. You've already committed 18 months of your life to this; it is essential you do not make an impulsive decision.
The first question that is crucial you answer is whether your perception of doing poorly in your PhD is founded or not. I know that at the moment, you may feel pretty convinced that success in your PhD is out of reach. But I would encourage you to put your concerns into context. Virtually everyone I know who has a PhD talks about the second year "blues" or "doldrums." The second year is a particularly tricky time in a PhD because you may feel overburdened with what still needs to be achieved and have the impression that your efforts have so far amounted to nothing. But often, what is at the root of this mid-PhD crisis is a lack of understanding about how a PhD is expected to develop -- rather than an inability of a PhD student to develop as a researcher.
Being half-way in your PhD time, you might feel that you should have "half a PhD" to show for your efforts, but PhDs don't develop in a linear fashion. I'd like to refer you to a good general guide to PhD progress from GRAD, which you can request directly by email . Your graduate school or careers services office may also have copies.
In short, the first year or two really are dedicated to laying out the foundations for a PhD. By now you should have a strong grasp of the context of your research, have a clear research aim, understand how to plan the whole project and individual experiments, and have set up all the basic techniques you need. If you have fallen short in one or two of these areas, you're in good company. But by the third year, you should be able to start generating data, and reap the benefits of all your efforts so far even though you didn't see tangible outcomes.
So I would encourage you to relate your situation to other PhD students around you, and to more senior scientists who've "made it." I also do think you need to talk to your supervisor about your progress -- and your feelings about how little headway you think you have made toward your thesis. Grit your teeth and be honest. Ask them for feedback on how you are developing as a researcher, and if they think you have a good chance of getting a PhD in the end.
Now, if after all these reality checks failure seems most likely, I agree there would be little point in pursuing a direction that may only be a dead-end. Even more so, I agree that it is best to choose an alternative career from a position of strength and not one of weakness. A failed PhD is not very attractive to employers, and you would be likely to find your options more limited than they are now.
However, and this is the most likely outcome, you might well realise that you may have good chances to pull it through. This is when your choice between continuing the PhD or taking a tangent becomes tricky.
What you should consider at this stage is what other career options you have available right now. If you have nothing else tangible in the pipeline, and especially if you have no idea what career you would like to go for, then I would encourage you to finish your PhD (provided your supervisor thinks you have got good chances of success). That will both leave you time to find out what you would enjoy doing and work out how to get there, while also developing skills that are of value to employers.
It may reassure you to know that more than 50% of PhD graduates choose to leave university life behind after their vivas. There was a recent GRAD survey  of people who left higher education, and almost 40% of the doctoral graduates who responded were working in non-research roles, demonstrating that a wide range of employers are interested in PhD graduates. As well as statistics, you will find in this report profiles of recent PhDs and comments from employers which I'm sure will make you realise how transferable PhDs are.
Now, the situation may well be that you have already lined up a real opportunity to start an alternative career which, after extensive research and careful consideration, feels right for you. Then leaving your PhD may be the best option for you indeed. It is key, however, to be aware that employers' reactions to your decision will be most strongly influenced by your attitude. If they see negative responses (like apologies or defensiveness), they will wonder if you did the right thing (you may regret your choice and go back), or whether you were at the heart of the problem.
If, on the other hand, you are upbeat and talk about the positive side of walking away (realising that your skills and strengths were best suited to this field; or your willingness to take control and make a difference to your future rather than continuing on the conveyor belt), then they will see someone who can make difficult decisions and has emerged from a stressful situation with optimism and determination --all great selling points!
Finally, you were also asking about converting your PhD into an MPhil, which at first look may appear like a good compromise in your decision to quit or not quit. But I doubt it would be a realistic option. Students who work toward a MPhil from the outset are given less ambitious projects and spend less time establishing the context and learning how to manage and carry out research. After 18 months, they would have finished their research, whereas you admit that you have little of substance to show at this stage. By the time you have written up an MPhil, you would probably be most of the way to your PhD.
As a whole, I would advise you not to leave your PhD unless you've got something good to move on to and feel very positive about it. But if this is not your situation, and you can find the drive to continue and succeed, you will develop valuable skills and gained the confidence to tackle almost anything.
Good luck in your career,